Analytical and Comparative Study for Solar Thermal Cooling and Photovoltaic Solar Cooling in the MENA Region By Younis Yousef Abidrabbu Badran A Thesis Submitted to the Faculty of Engineering at Cairo University and Faculty of Electrical Engineering and Computer Science at Kassel University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Renewable Energy and Energy Efficiency Faculty of Engineering Cairo University Kassel University Giza, Egypt Kassel, Germany March, 2012
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Analytical and Comparative Study for Solar Thermal Cooling ... · V Abstract In this thesis, a comparison and analyses of solar thermal and solar photovoltaic (PV) air-conditioning
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Analytical and Comparative Study for Solar Thermal Cooling and Photovoltaic Solar Cooling in the MENA
Region
By
Younis Yousef Abidrabbu Badran
A Thesis Submitted to the Faculty of Engineering at Cairo University
and Faculty of Electrical Engineering and Computer Science at Kassel University
in Partial Fulfillment of the Requirements for the Degree of
Master of Science in
Renewable Energy and Energy Efficiency
Faculty of Engineering
Cairo University Kassel University Giza, Egypt Kassel, Germany
March, 2012
Analytical and Comparative Study for Solar Thermal Cooling and Photovoltaic Solar Cooling in the MENA
Region
By
Younis Yousef Abidrabbu Badran
A Thesis Submitted to the Faculty of Engineering at Cairo University
and Faculty of Electrical Engineering and Computer Science at Kassel University
in Partial Fulfillment of the Requirements for the Degree of
Master of Science in
Renewable Energy and Energy Efficiency
Reviewers Supervisors
Prof. Dr. Adel Khalil Member Mechanical Power Engineering Department Faculty of Engineering, Cairo University
Dr.-Ing. Norbert Henze
Systems Engineering and Grid Integration Department Head of group. Engineering and Measuring Technology Fraunhofer Institute IWES, Kassel, Germany
Prof. Dr. Albert Claudi Member Faculty of Engineering and Computer Science Kassel University
Dipl.-Ing. Siwanand Misara Member Group of Engineering and Measuring Technology Fraunhofer Institute IWES, Kassel, Germany
In this thesis, a comparison and analyses of solar thermal and solar photovoltaic (PV)
air-conditioning technologies for a Typical Single Family House (TSFH) in two different
MENA climates, Aswan-Egypt and Aqaba-Jordan, are performed. The building cooling
demand is firstly obtained from annual building simulation in TRNSYS software. Based
on these simulation results, three scenarios are designed in order to compensate the
TSFH’s annual cooling demand in each selected climate. These scenarios are solar
thermal air-conditioning with storage (absorption chiller), PV air-conditioning without
storage and PV air-conditioning with storage. The cooling compensation is simulated by
Matlab-Simulink for each scenario.
TRNSYS simulations for Aswan-TSFH and Aqaba-TSFH respectively demonstrate that
the maximum cooling load demand during summer season are: 13.9 kW and 15.3 kW;
the annual cooling energy demands are: 44,330 kWh/year and 43,490 kWh/year which
represents 97.5 % and 96.3 % of the total annual energy consumption (heating and
cooling). On the other hand, Matlab-Simulink demonstrates that the total annual
percentage of cooling energy compensation (direct plus storage) difference between the
PV and thermal with storage scenarios does not exceed 1 % in both cases. However,
differences exist between the two scenarios. The performance of daily direct cooling
compensation by the PV air-conditioning scenarios is more efficient than in the thermal
air-conditioning scenario. The direct cooling compensation percentage for the Aswan-
TSFH and the Aqaba-TSFH respectively are 39.3 % and 35.8 % for the PV air-
conditioning scenarios and 30.8 % and 30.9 % for the thermal air-conditioning scenario.
The compensation by the storage are 10.7 % and 7.3 %, by the PV air-conditioning with
storage scenario and 20.1 % and 11.9 %, by thermal air-conditioning with storage
scenario for the two cases respectively.
The PV air-conditioning scenario with storage behaves and compensates the cooling
demand better than the solar thermal air-conditioning with storage scenario and needs
less storage to cover the same amount of cooling load demand. However, the storage
system in the PV air-conditioning scenario is minor and the direct compensation is
major. That is vice versa in the thermal air-conditioning scenario. This research can be
extended to compare and analyze the scenarios in terms of primary energy, economic
analysis and different buildings. Moreover, the future cost reduction by learning curves
of both technologies can influence the economic feasibility.
VI
Contents
Acknowledgements ............................................................................................................................... iv
Abstract ...................................................................................................................................................... v
List of Figures.......................................................................................................................................... ix
List of Tables .......................................................................................................................................... xii
List of Symbols ..................................................................................................................................... xiii
List of Abbreviations .......................................................................................................................... xvi
Figure 2.4: sketch of Typical Single Family House(TSFH) in MENA regions plan, [20]. ......9
Figure 3.1: Zones of TSFH model in TRNBuild. .................................................................................... 16
Figure 3.2: Aswan-TSFH model (Type 56) with all the required components and
connections in TRNStudio. ............................................................................................................................. 18
Figure 3.3: Aqaba-TSFH model (Type 56) with all required components and connections
in TRNStudio. ........................................................................................................................................................ 19
Figure 3.4: Yearly cooling and heating energy demand for the Aswan-TSFH and Aqaba-
Figure 3.5: Monthly cooling and heating energy demand in (kWh) for the Aswan-TSFH
and Aqaba-TSFH. ................................................................................................................................................. 22
Figure 3.6: Yearly Cooling and heating demands distribution(kW) for the Aswan-TSFH.
In these equations the Ss,i, is the radiative heat flux absorbed at the inside surface, is
the inside surface area, is the view factor to the sky, artificial temperature
node, is referred to the resistance. The Latent heat gain by the ventilation or
infiltration is calculated by using [28], [31], [32]:
………………………………………………………………………..…………….…..(3.9)
For more details about the mathematical model which are used by TRNSYS simulation,
see TRNSYS16 manual [33].
16
3.2.2 TSFH Modeling with Type56 and TRNBuild TRNBuild is used to enter the TSFH input data and to create the TSFH description file
(*.bui). This file includes all the information required to simulate the building where
(*.bui) file used to generate three new files: the (*.bld)2, (*trn)3 files which are used by
TYPE 56 during the simulation process in TRNStudio program and information
file(*.inf)4)
As shown in Figure 3.1, TRNBuild allows the users to specify all the building structure in
details that is needed to simulate the thermal behaviour of the TSFH such as geometry
data, wall construction data, windows data, etc. Furthermore, it needs SCHEDUALE
information which define the internal heat gain from the equipment and occupants
during the day in the TSFH.
Figure 3.1: Zones of TSFH model in TRNBuild.
2 The file containing the Geometric information about the building. 3 The file containing the wall transfer function coefficients. 4 An informational file.
17
This section includes a brief description of steps for the TSFH modelling with TYPE 56
and TRNBuild which are followed in this study.
As shown in Figure 3.1, the TRNBuild manager defines the project details: TSFH
orientation, iconic properties which define the parameter value for software calculation
such as air density, specific heat of air etc. Inputs icon which is used to add the required
INPUTS to TYPE 56 (such as, control strategies etc.) whereas the outputs icon describe
the OUPUTS of TYPE 56 such as sensible energy demand of zone etc. where this is the
last step of the building description.
The TSFH zones thermal definition step include the adding zone walls and windows in
addition to its thermal description (see Tables 2.1 and 2.2): defining the materials that
will make up the layers of the wall (from internal zone to external) in addition to the
wall area, geography (external and internal), thermal conductivity etc., defining the
materials that will make up the layers of the window and adding (its thermal properties,
area and orientations etc.).
After the TSFH zones definition step, inserting the TSFH zones required regime, data
step has been followed which includes: infiltration and ventilation data, heating and
cooling set points, internal gain setting data, comfort and Humidity. In this study
,Chapter 2 includes all of the required data for the second step where the infiltration
and ventilation data listed in Table2.3, the internal gain is considered based on ISO 7730
standard. Cooling set point is 24 0C dry bulb and a maximum of 50–65 % relative
humidity . The Heating set point is 20 0C dry bulb and 30 % relative humidity.
Defining the outputs needed from TYPE 56, in this step the output can be selected from
the list such as, sensible energy demand (cooling and heating) of building, air
temperature of zone, etc. In this study, the sensible energy demand of three bedrooms,
living room, guest room and kitchen is defined as outputs for TYPE 56.
The final step in the running model is to generate the TYPE 56 files: (*.bui) file used to
generate three new files: the (*.bld)5, (*trn)6 files which are used by TYPE 56 during the
simulation process in TRNStudio program and information file (*.inf)7.
5 The file containing the Geometric information about the building 6 The file containing the wall transfer function coefficients
18
3.2.3 TSFH Modeling with Type56 and TRNStudio After the TSFH Model in TRNBuild is created and the TSFH description file (*.bui) is
generated, the TSFH modelling with Type56 and TRNStudio started to complete the
simulation of the TSFH thermal cooling and heating loads demands. The brief
description of the simulation steps which are followed in this software (TRNStudio) are
as described as follows:
The first step, creating a new Multizone building project and all its necessary
parameters have been entered (such as drawing TSFH plan, setting zone properties,
setting window,...etc). Once the created project has been finished the simulation studio
will create a multi zone building description (stored in a .BUI file), translate the TSFH
description file (*.bui) file to the internal files necessary for simulation (*.bld8, *trn9
files) from TRNBuild program, create a simulation project (stored in a .TMF file) and
open it in the simulation studio [33]. So a simulation with the important components
and links for the first run are automatically generated.
Figure 3.2: Aswan-TSFH model (Type 56) with all the required components and
connections in TRNStudio.
7 An informational file 8 The file containing the Geometric information about the building 9 The file containing the wall transfer function coefficients
19
Figure 3.3: Aqaba-TSFH model (Type 56) with all required components and
connections in TRNStudio.
Figure 3.2 and Figure 3.3 show that the TSFH model (Type 56) with all required
components and connections in simulation studio for Aswan and Aqaba respectively.
The studio simulation has been started to specify the values for the variables in the
components of the TSFH model then determines how data flows from one component to
another (such as solar radiation data flows from TYPE 16e to TYPE 56 ). This data flow
is indicated by a link between two components in the Assembly Panel window.
Assembly Panel window includes the simulation components as shown in the right hand
side in Figure 3.2 and Figure 3.3. However, the link shown on the assembly panel is
purely informational. So it must specify the details of the link between two components
to actually flow data from one component to another [33].
As known in Chapter 2, the meteorological data of Aswan city in TMY and EPW format
and its hourly horizontal solar radiation data. In addition, regarding the TSFH geometry,
the direct and diffuse radiation of every hour should be determined. Then it must be
converted into hourly tilted radiations depending on the sun position in the sky and on
the TSFH surface’s slope from the horizontal plan. So TYPE 15-3, weather data reading
and processing have been chosen for the Aswan-TSFH model in order to read the Aswan
20
meteorological data file and to calculate the hourly solar radiation (direct plus diffuse)
regarding to the TSFH surface’s slope and on the sun position in the sky. After that data
has been processed, it will be provided from TYPE 15-3 to TYPE 56 in order to simulate
the TSFH cooling and heating demands.
In the simulation case of Aqaba-TSFH, there is a difference because the metrological
data file has been in Excel format. So the TYPE 9e has been chosen in order to call and
read the excel data file which provides this data through the link to TYPE 16e. The TYPE
16e completes the data processing before delivering it to TYPE 56 as in Aswan-TSFH
case. In this step, the Reindl model has been chosen in TYPE 15-3 and TYPE 16e in order
to calculate the tilted solar radiation. For more details about Reindl mathematical
model, see the TRNSYS16 module [33].
As shown in the above figures, TYPE 33e has been chosen for both cases. ‘‘This
component takes as input the dry bulb temperature and relative humidity of moist air
from the processing data component and calls the TRNSYS Psychrometrics routine,
returning the following corresponding moist air properties: dry bulb temperature, dew
point temperature, wet bulb temperature, relative humidity, absolute humidity ratio,
and enthalpy’’ [33]. This data is transferred to TYPE 56 to use it in the cooling and
heating demand calculations.
TYPE 69b is selected for each model in order to determine the effective sky
temperature, which is used by TYPE 56 to calculate the long-wave radiation exchange
between an arbitrary external surface of the TSFH and the atmosphere. TYPE 65 is
online graphics component which is used to display selected system variables while the
simulation is progressing [33].
Final step in the TRNStudio simulation is the running step, where the cooling load is
calculated in 15 minutes time step by TRNSYS software for the two case studies. Then
the cooling and heating load demand simulation results for the TSFH has been provided
for both cases.
21
3.3 Thermal Cooling Load Simulation Results and Analysis of Results
As mentioned before, the major objective of this simulation is to determine the cooling
load of a typical single family house in two different climate locations in the MENA
regions: Aswan city in Egypt and Aqaba city in Jordan . The discussion and analysis on
simulation results concentrate mainly on sensible cooling load demand of TSFH (three
bedrooms, living room, guest room and Kitchen). The simulation results and the
analysis of the results are documented in subsequent subsections.
3.3.1 The Annual Energy Consumption
This section discusses the annual cooling load consumption for both cases, Aswan-TSFH
and Aqaba-TSFH. Figure 3.4 and Figure 3.5 below diagram the total annual and monthly
cooling and heating energy consumptions for the aforementioned cases respectively.
Figure 3.4: Yearly cooling and heating energy demand for the Aswan-TSFH and
Aqaba-TSFH.
The simulation result in Figure 3.4 shows the annual energy consumption where the
total cooling load energy are : 44,330 kWh/year and 43,490 kWh/year; the total heating
load energy are: 1114 kWh/year and 1635 kWh/year for the Aswan-TSFH and the
Aqaba-TSFH cases respectively. On the other hand, 97.5 % and 96.3 % of the annual
energy consumption are cooling load for the two cases respectively.
: is the collector’s efficiency in design condition
OP : coefficient of performance
For our case, G=800 W/m2 coll
=50%, OP=0.7 and the specific design collector’s area
resulted is Acoll,Spec =3.5 m2 for a 1kW of cooling capacity.
According to this rule of thumb, the solar collector area for the solar thermal air-
conditioning scenario is designed. The solar radiation for the two locations, Aqaba city
and Aswan city is approximately G=1000 W/m2 in summer (see Figure 2.1). This means
a specific collector’s area is Acoll,Spec = 3.5 m2 for 1kW cooling capacity which is needed
for this scenario.
As discussed in chapter 3, the maximum cooling load demand is 13.9 kW and 15.3 kW
for Aswan–TSFH and Aqaba-TSFH respectively. The assumption is made for both cases
that the maximum cooling load demand is 15 kW in each case. So, the area of the
collector needed for the system is 42 m2.
10 A solar air-conditioning system can be either a standalone autonomous system where all energy input is from solar or a solar-assisted air-conditioning system where partial energy input is supplied from solar.
44
In order to simplify the comparison between the PV air-conditioning scenarios and
thermal air-conditioning scenarios which is a major objective of this study, the solar flat
plate collector is designed for 45m2 which is equal to the PV-array area in the PV air-
conditioning scenarios.
Flat plate collectors are fixed and there is no tracking system. The collectors should be
oriented directly towards the equator. The collector’s location in the northern
hemisphere should be facing the south and vice-versa in order to maximize the amount
of daily and seasonal solar energy received by the collector. The optimal tilt angle of the
collector is an angle equal to latitude of its location [51]. However, in summer the tilt
angle should be smaller than the latitude to receive more solar radiation.
Table 5.1 : Parameters of the flat plate collector, [52].
Parameter Flat plate collector Unit
78.4 [%]
C1 4.28 [W/m2K]
C2 0.014 [W/m2K2]
Surface area 2.69 [m2]
45
Storage Tank
The solar photovoltaic air-conditioning system stores the excess DC in batteries.
Similarly, It is necessary to use a thermal energy storage tank, either heat or cold
storage in thermal air-conditioning system.
According to [36], the thermal energy from the collector can be stored to be used when
needed by the air-conditioning (heat storage). Alternatively, the cooling product by the
air-conditioning can be stored in a low temperature (below ambient) thermal storage
unit (cold storage). That’s to provide cold energy for a few hours in the afternoon when
solar radiation already decreases but internal cooling load demand is still high.
These two alternatives are not equivalent in capacity, costs or effect on the overall
system design and performance. The required capacity of a cold storage tank is less than
that required of a heat storage tank because the heat storage has a higher conversion
efficiency than the cold storage tank [36]. In addition, heat storage tanks can be used for
other applications for example domestic hot water or space heating.
There are two technologies for hot water storage tanks which can be used. Either with
thermal stratification or without. Stratification means moving the thermal heat from
layers of cold water at the bottom of the tank to the hot water at the top of the tank.
That will increase the performance efficiency of the system.
According to [6], in order to achieve a solar fraction of 80 % for the given cooling load
profile, a collector aperture area of 48.5 m2 and a storage tank volume of 2 m3 is
required if the generator is always operated at an inlet temperature of 85 0C.
This study analyzes a solar thermal air-conditioning system (Lithum-Bromide water
absorption chiller with a COP of 0.7 and a nominal cooling capacity of 15 kW ) in
Madrid. Madrid has a Mediterranean climate similar to the selected locations in this
study ,where the solar radiation reaches 1000 W/m2 in summer.
In this study the stratification of a hot water storage tank volume is 2m3. The tank is
produced by KWB company in Germany (see Table 5.3) [53]. The tank parameters are
listed in Table 5.3.
According to [50]and [35], high temperature differences between the inlet and outlet of
a collector are not recommended in a solar air-conditioning systems. The basic reason is
46
that thermally driven chillers in general work at comparatively low temperature
differences between inlet and outlet, e.g. 10 0C. Therefore, in this study 20 0C
temperature difference in the storage tank is assumed.The storage tank has 20 0C
temperature nodes to simulate stratification with minimum temperature equal to the
chiller outlet hot water temperature of 75 0C and the maximum temperature of 95 0C.
Back-up System
When there is no enough solar radiation (e.g. at evening, night or on cloudy days), it will
be a necessary to have a back-up system for the cold production or to allow the solar
air-conditioning system to continue.
Two different back-up approaches can be used to achieve this objective, either back-up
heating or cooling systems. The back-up heating system usually uses burners (oil, gas or
pellet) or electric heater connected directly to the heat storage tank. The back-up
cooling system usually uses conventional vapour pressure cooling devices.
In this study, a back-up electric heater supplies the storage tank with heat whenever the
storage tank temperature drops below the set point temperature required for driving
the sorption chiller (85 0C). This gives stability for the cooling production of the chiller
especially in the afternoon(see Table 5.3).This choice (back-up heater)and not back-up
cooling system has been built based on two arguments. Firstly compared with back-up
cooling system, the back-up heater support the absorption chiller to going on even if the
hot water which delivered by the collectors is lower than the minimum operation
temperature of the absorption chiller, this leads to increase the absorption chiller
operation time during the presence of solar radiation. which means higher solar gain
and benefit . The second argument the price of back-up heater system is much less than
the back-up cooling system.
47
5.3.1.2 Absorption Chiller
Most of the thermally driven cooling system and solar assisted air-conditioning systems
installed today are based on absorption chillers [34], [35].
The absorption chillers are used to produce chilled (cold) water which can be used for
any type of air-conditioning equipment to cover the cooling load demand in the
building.
Physical Description
Figure 5.5: Schematic diagram for an absorption chiller for chilled water
production, [37].
Figure 5.5 depicts the schematic diagram for the working principle of absorption chiller
systems. ‘‘They are similar to a mechanical compression cooling system with respect to
the system components evaporator and condenser. In a mechanical compression
cooling system, a mechanical compressor is employed in order to produce the pressure
differences and to circulate the refrigerant. Whereas the absorption chiller uses a heat
source. The absorption chiller consists of an absorber, a pump, a heat exchanger, a
generator and a throttle valve instead of a mechanical compressor.The steps description
12 For more details about the wet cooling tower system see the schematic diagram and the description of this system in according to [37] in Appendix D.
52
5.3.3 System Simulation and Methodology The simulation provides useful information about the long-term performance of a solar
thermal air-conditioning system. This section describes the simulation steps for the
solar thermal air-conditioning scenario by the using Matlab-Simulink for both cases of
Aswan-TSFH and Aqaba-TSFH.
Simplifications are made by keeping the coefficient of performance of the absorption
chiller (COPABCH) constant at 0.71, by assuming a constant heating water temperature of
85 oC re-cooling water temperature (30 oC) and a cold water temperature (11 oC) as
indicated by the manufacturer (see Table 5.2).
The simulation process is done step by step for each case, starting with the loads that
have to be compensated by the chiller depending on the cooling load demands. In the
first step, the hot water and the power consumption of the chiller together with the
cooling tower is calculated by assuming the cooling power demands Pcool- load c and the
coefficient of performance for the absorption chiller COPABCH . The heat power supply
required by the absorption chiller P hABCH h is calculated by using the following equation
Direct compensation compensation by storage Back-up cooling Energy
Aqaba Aswan
Co
olin
g En
ergy
78
collector to the ambient air in Aqaba than in Aswan , where the collector temperature is
designed to work at 85 o C and the outside air temperature in the Aqaba is lower than in
Aswan during the summer and a more fluctuation (see Figure 2.2 ).
In winter for both cases the cooling energy demand is fully covered especially in
November, December, February and October. This in turn means the cooling demand at
the evening and at night happens by the storage participation without requiring a
external back-up cooling. That is due to the cooling demand in winter being less than
the summer’s .
The month of March fulfil cooling demands where the compensation by the storage is
higher than the direct. This in turn means a better overcoming of night demand in both
cases is obtained in this month of the year.
Generally, the Aswan-TSFH case has a higher external back-up cooling in April and
October than the Aqaba-TSFH case due to a higher night cooling demand in these
months.
In Aqaba-TSFH case, the month of October has a higher contribution by the storage to
compensate the cooling energy demand than in Aswan-TSFH case. This is because of a
higher night cooling in Aqaba-TSFH than in Aswan-TSFH. On the other hand, the storage
in this month reduces the mismatching between the cooling production and the demand
more efficiently in Aqaba-TSFH case.
79
6.2.2.3 Solar Fraction
As discussed in Chapter 5, solar fraction (SF) is a key factor in sizing the solar thermal
system which works as the source of energy to drive the absorption chiller. It is
dependent on many factors such as the load demand , the collector, the storage size ,the
operation ,and the climate and hence SF is calculated for the two cases.
Figure 6.21: Annual solar fraction for the solar thermal air-conditioning system
scenario in Aswan-TSFH and Aqaba-TSFH.
Figure 6.22: Monthly solar fraction for the solar thermal air-conditioning system
scenario in Aswan-TSFH and Aqaba-TSFH.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Aqaba Aswan
So
lar
frac
tio
n [
%]
0
0.2
0.4
0.6
0.8
1
Sola
r fr
acti
on
[%
]
JAN FEB
MAR APR
MAY JUN
JUL AUG
SEP OCT
NOV DEC
Aswan Aqaba
80
Figure 6.21 and Figure 6.22, give an overview of the monthly and yearly solar fraction
that can be obtained for the solar thermal system under a solar thermal air-conditioning
system with a storage scenario designed for both locations under the same storage size
of 2 m3 and a collector area of 45 m2. The graphs are valid for a TSFH in the two selected
locations, Aqaba and Aswan, and for the flat plate collector under the system design
boundary conditions of this study.
As shown in Figure 6.21, the yearly SF is 50% and 41% for Aswan and Aqaba cases
respectively. While comparing those SF values by which the Aswan case is higher than
Aqaba case. This is due to the high solar radiation. As a result, much of the heat
produced by the collector can be stored. Therefore, better overcoming of the solar gain
and load mismatching is obtained. In addition, we can achieve a better overcoming of a
night demand in Aswan-TSFH case. Further more in Aqaba-TSFH case has higher heat
losses from the collector and the storage tank than Aswan-TSFH, this due to low
ambient air temperature in Aqaba city.
In summer(see Figure 22), the higher SF is obtained in Aswan than in Aqaba case. As
already discussed, it is because the Aswan-TSFH case has higher solar gain and it means
better to overcome the night demand which is obtained by the contribution of the
storage (see Figure 6.20). The graph could help in taking a technical decision. The
storage tank size for the solar thermal air-conditioning system scenario in Aswan-TSFH
could play for the compensation of a cooling load better than in Aqaba-TSFH system
scenario.
In winter for both cases(see Figure 22), the solar fraction reaches 100% which in turn
means the cooling load demand has been covered fully 100% by the solar thermal air-
conditioning system without the need to external back-up cooling. This due to a low
cooling demand and a high solar energy gain by the collector in this period (see Figure
6.20 ). But it should be clear that the Cooling energy consumption is very little or
negligible in some months, such as November, January and February. As a result, most
of the heat produced from the collectors will be a waste energy.
81
6.3 Thermal Air-conditioning Scenario Versus PV Air-conditioning
Scenarios
6.3.1 The Direct Cooling Production Load Performance
This section discusses and analyzes the solar thermal air-conditioning scenario versus
solar PV air-conditioning scenarios based on the performance of the cooling production
on the weekly and daily bases(as the systems without storage).
Weekly Performance:
Figure 6.23 and Figure 6.24 illustrate the weekly cooling production load for the solar
PV air-conditioning scenarios versus thermal air-conditioning scenario where the
systems as without storage. Generally, these samples represent the weekly cooling
compensation especially in the summer where there are high cooling demands.
Figure 6.23: PV air-conditioning versus solar thermal air-conditioning, cooling
production performance in Summer Week for Aswan-TSFH.
82
Figure 6.24: PV air-conditioning versus solar thermal air-conditioning, cooling
production performance in Summer Week for Aqaba-TSFH.
Figure 6.23 and Figure 6.24 generally show the following for each day in the week for
both cases: Aswan-TSFH and Aqaba-TSFH.
The daily cooling production along the week by the thermal air-conditioning scenarios
has a higher peak curve than the PV air-conditioning scenarios. In addition, the excess
cooling production which is above the cooling load demand curve of the solar thermal
air-conditioning scenario is higher than the curve for the solar PV air-conditioning
scenario. That could lead us to say that the storage system for the thermal air-
conditioning scenario is more important and efficient than the PV scenarios especially
in summer for Aswan-TSFH.
The daily cooling production curve which is produced by the solar PV air- conditioning
starts in the morning before the curve of the solar thermal air-conditioning system
scenario and ends at the evening and vice versa. This leads to a conclusion that the daily
direct cooling compensation by the PV air-conditioning scenario is more efficient than
the thermal scenario. In another way, the daily direct cooling energy compensation
which is the area under the cooling production curve, under the cooling demand curve
in PV air-conditioning scenarios is higher than in the thermal air-conditioning scenario.
83
In addition, the daily external back-up cooling energy needed is the remaining area
under the cooling demand curve after deducted the area of direct cooling compensation
energy. This external back-up cooling energy is higher than the direct compensation
energy for both scenarios. That’s due to a higher night cooling demand. Furthermore,
the external back-up cooling needed for the PV-system is lower than for the thermal
system. which leads to say that the thermal system as without storage has a higher
mismatching with the cooling load demand than in the PV-system without storage.
Daily Performance:
After the weekly discussion and analysis, this Section discusses and analyzes the daily
performance of the cooling production in order to link the results with the main
technical and physical reasons. And this leads to clarify the weekly results in the whole
scenarios’ results.
Figure 6.25:PV air-conditioning versus solar thermal air-conditioning, cooling
production performance in Summer day for Aswan-TSFH.
84
Figure 6.26: PV air-conditioning versus solar thermal air-conditioning, cooling
production performance IN Summer day for Aqaba-TSFH.
Figure 6.23 to Figure 6.26, diagram that the PV air-conditioning scenarios have higher
direct cooling compensation than the one by the solar thermal air-conditioning
scenario, the cooling production curve by the PV air-conditioning scenario starts earlier
in the morning than the thermal air-conditioning scenario. Furthermore, at the evening
the curve of the PV air-conditioning scenarios ended at a zero value and late compared
with the curve of thermal air-conditioning scenario. In addition approximately, in
morning and at evening, the cooling compensation curve of the PV air-conditioning
scenario is higher than that of the thermal air-conditioning scenario in this period . The
reasons are summarized below.
The reasons are, firstly the thermal collector has higher efficient compared to PV
module where the solar collector efficiency is around 50% and PV module is around
14% . But not too much due to the COP of compressed chiller and Absorption chiller is
completely different. Where the COP is nearly 3 for the compressed chiller in the PV air-
conditioning scenario and it is around 0.7 for the absorption chiller in the thermal air-
conditioning scenario, this lead to say in the direct cooling compensation, the overall
system efficiency of PV air-conditioning scenarios is higher than the one by the solar
thermal air-conditioning scenario.
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The second reason, the high thermal losses from the flat plate collector in thermal air-
conditioning scenario to the sounding outside air, where its temperature is lower in the
morning and at the evening compared with the noon. In addition, the thermal losses
from the hot water storage tank. As discussed in Chapter 5, where the solar thermal
collector is designed to work at a temperature as high as 85 0C in order to drive the
adsorption chiller. That leads the solar flat collector to start working late in the morning
and ended earlier in the evening especially when the thermal losses are higher than the
solar gain from the collector as designed in this study.
The third reason, in the morning and at the evening, the ambient air temperature is
lower than the noon’s. The PV module works with a high efficiency where the operation
temperature of the module is low due to a high thermal heat transferred to the ambient
air. And hence a low thermal effect on the PV module efficiency.
In addition, in the morning and at the evening there is a high reflection and diffused
radiation compared with a noon and in turn a higher electric power gain from the PV
module. On the contrary, the diffused and reflected radiation are not so sufficient to
produce heat by flat plate collector.
At noon of the day, the solar thermal air-conditioning scenario is more efficient to
produce a cooling load than the PV air-conditioning scenario. But most of the cooling
compensation by thermal air-conditioning scenario in this period exceeds the cooling
demand. As discussed before, the storage system is more important for thermal air-
conditioning scenario than the PV air-conditioning scenario.
The reason for this result is the flat plate collector works at noon with the highest
efficiency because of a higher solar radiation which increases the solar gain as hot water
in addition to a small thermal heat losses from the collector at this period, where the
ambient air temperature is higher compared with the morning and the evening. In
addition the peak cooling demand occurs at noon.
On the contrary at noon, the PV module efficiency reduces and stops due to the thermal
effect, where the module operation temperature is high by time the ambient
temperature is high . This low driving temperature reduces the heat transfer from the
module to the ambient air.
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Comparison Between Aqaba-TSFH Case and Aswan-TSFH Case:
As shown from Figure 6.23 to Figure 6.26, there are generally two major differences in
the performance of the cooling production by the thermal and PV scenarios as without
storage, for both the Aswan-TSFH case and Aqaba-TSFH case. These differences are
elaborated below.
The first difference in all scenarios , the Aswan –TSFH case has a higher extra cooling
production compared with Aqaba-TSFH due to a higher solar radiation in Aswan
especially in the summer season ( see Figure 2.1).
Secondly in all scenarios , the direct cooling production curve behaviour for the Aswan-
TSFH is more thin during the day than the Aqaba-TSFH. Besides, the Aswan-TSFH case
is mismatching a lot between the cooling compensation and the cooling load demand
than the Aqaba-TSFH case.
That’s due to the behaviour of the solar radiation in each city. In addition, a higher
diffusion and reflected solar radiation is observed in Aqaba city than in Aswan city
especially for this boundary condition of this study. Where an immense reflected solar
radiation in Aqaba city comes from the collector tilted angle, designed in this study,
29°31' which is higher than 23°54' for Aswan case. That in turn means a higher ground
reflected radiation which is collected by the collectors in Aqaba. In addition, the Aqaba
city is near the Red Sea and therefore has a higher air humidity compared with Aswan
(see Figure 2.3 ). This then leads to an increase in the diffused radiation in Aqaba city.
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6.3.2 Annual Cooling Compensation Energy Percentage Figure 6.27 and Figure 6.28 illustrate the yearly percentage of the direct cooling energy
compensation, the compensation of the cooling energy by storage and the external
back-up cooling energy which is covered by the grid for each scenario. This percentage
is calculated based on daily energy yield compensation in order to calculate the yearly
cooling energy compensation for each case study, Aswan-TSFH and Aqaba-TSFH . SO as
to make a comparison between the scenarios.
Figure 6.27: Percentage of cooling Energy compensation by the three scenarios for
Aswan-TSFH.
30.8% Direct copensation
20.1% Compensation by
storage
50.1% Backup compensation
Solar Thermal air-conditioning system with storage
39.3% Direct
copensation
10.7% Compensation by storage
50% Backup
compensation
Solar PV air conditioning system with storage
39.3% Direct
copensation
60.7% Backupcompens
ation
Solar PV air conditioning System without storage
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Figure 6.28: percentage of cooling Energy compensation by the three scenarios for
Aqaba-TSFH.
From Figure 6.27 and Figure 6.28, several observations are made below.
The yearly direct cooling compensation percentage of the PV air-conditioning scenarios
is 39.3% and 35.8% for the Aswan-TSFH and for the Aqaba-TSFH cases respectively.
The above mentioned percentages are higher than the direct cooling compensation
percentage by the thermal air-conditioning scenario, 30.8 % and 30.9 % for the Aswan-
TSFH and for the Aqaba-TSFH cases respectively. This in turn means a higher
mismatching between the direct cooling compensation and the cooling demand in the
thermal air-conditioning scenario.
30.9% Direct
copensation
11.9% Compensation by
storage
57.2% Backup compensation
Solar thermal air-conditioning system with storage
35.8% Direct
copensation
7.3% Compensation by storage
56.9% Backupcompensa
tion
Solar PVair-conditioning system with storage
35.8% Direct
copensation
64.2% Backup
compensation
Solar PV air-conditioning System without storage
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As discussed before, the main reason is a higher daily direct cooling compensation in
the morning and at the evening by the PV air-conditioning scenarios than the thermal
air-conditioning scenario. That’s due to the COP of compressed chiller and Absorption
chiller is completely different where the COP of the compressed chiller is around 3 and
it is around 0.7 for the absorption chiller. That leads to enhanced the overall system
efficiency of the PV-air conditioning scenarios comparatively with thermal air-
conditioning scenario. In addition at the evening and in the morning, low ambient air
temperature makes the thermal losses be higher than the solar gain from the flat plate
collector in addition to the thermal losses storage tank. In addition, PV module works
early with a higher efficiency at low solar radiation in the morning and the evening time.
Yearly, the total percentage cooling energy compensation by direct and storage in solar
thermal air-conditioning system with storage scenario is 50.9 % and 42.8 % for Aswan-
TSFH case and for the Aqaba-TSFH case respectively. The total compensation by PV air-
conditioning with storage scenario, 50 % and 43.1 % are respectively for Aswan-TSFH
and for Aqaba-TSFH cases. From these results, the percentage difference between the
two scenarios does not exceed 1 % in both cases(Aswan-TSFH and Aqaba-TSFH)and in
turn there is no big difference between the two scenarios based on the cooling demand
and the boundary condition of this study. that due the same reason which mentioned
above, the COP effects on the overall system efficiency.
The percentage of the cooling energy compensation by the storage in the thermal air-
conditioning scenario is 20.1 % and 11.9 % for Aswan-TSFH and for Aqaba-TSFH
respectively. The aforementioned percentages are higher than the percentage
compensation by the storage in PV air-conditioning with storage scenario, 10.7 % and
7.3 % for Aswan-TSFH and Aqaba-TSFH respectively. That’s because of significantly
excess output power, from the thermal air-conditioning system with storage scenario
compared with the PV air-conditioning system with storage scenario, where the
contribution power which is produced by the flat plate collector is higher than the
output power of the PV module at noon. This contribute to compensate the night cooling
demand throughout the storage.
This helps to make a technical decision based on the study boundary condition. We can
deduct that the storage technology for thermal air-conditioning scenario is more
efficient to improve the whole system’s efficiency than a PV air-conditioning scenario.
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7. Conclusions and Future Research
7.1 Conclusions
The traditional air-conditioning is one of the main consumers of electrical energy today
in the MENA region. However, this region has a huge solar energy potential with an
average DNI13 of 2,334 kWh/m2/year and with average daily sunlight exceeding 8.8
hours [4]. Solar air-conditioning technology is definitely a solution to cover the cooling
demand for this hot and sunny region. The present study analyzes and compares the
solar thermal air-conditioning technology and the photovoltaic air-conditioning
technology under two different locations in the MENA region (Aswan, Egypt and Aqaba,
Jordan). That is based on the cooling demand for the reference building (TSFH ) in these
regions.
Cooling load demands:
The thermal load demands for the reference building (TSFH) in each location were
determined by TRNSYS software. The following points can be concluded:
The maximum cooling load demand during the summer season are: 13.9 kW and 15.3
kW for Aswan-TSFH and Aqaba-TSFH respectively. For both cases, the cooling demand
occurs for ten months while the heating demand is only required in two months. The
annual cooling energy demands are: 44,330 kWh/year and 43,490 kWh/year for the
Aswan-TSFH and the Aqaba-TSFH respectively which represents 97.5 % and 96.3 % of
the total annual energy consumption (heating and cooling). That shows the importance
of cooling compared to heating in these locations.
The performance of the cooling load during a summer day shows a huge cooling
demand (approximately 8 to 10 kW) during the night. Therefore, it is necessary to cover
the night cooling demand as well as the day time in these regions.
13 Direct Normal Irradiance
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Solar Thermal Air-conditioning Scenario and PV Air-conditioning Scenarios :
The cooling production and compensation of each scenario is determined by Matlab-
Simulink for three scenarios:
Solar thermal air-conditioning with storage scenario includes a single water/Lithium-
Bromide absorption chiller with 15 kW nominal capacity and requires 85 oC driving
temperature, 45 m2 flat plate collectors, a stratified storage tank with 2 m3 volume and
an electric heater as back-up system.
Two PV air-conditioning systems with and without storage scenarios were designed
with a 45 m2 of PV-array, a compressed chiller and the grid as a back-up system. The PV
air-conditioning system with storage includes additionally 8 batteries.
Form the analysis and comparison between the thermal and the PV scenarios the
following points can be concluded:
The total annual percentage of cooling energy compensation (direct14 plus storage15) by
the solar thermal air-conditioning system with storage scenario is 50.9 % and 42.8 %
for Aswan-TSFH and for Aqaba-TSFH respectively. The compensation by the PV air-
conditioning with storage scenario which is 50 % and 43.1 % respectively for Aswan-
TSFH and for Aqaba-TSFH. The percentage difference between the two scenarios does
not exceed 1 % in both cases. However, there are differences in the direct cooling
compensation and the compensation by the storage:
1. The yearly direct cooling compensation percentage of the PV air-conditioning
scenarios is 39.3 % and 35.8 % for the Aswan-TSFH and for the Aqaba-TSFH
respectively. The aforesaid percentages are higher than the direct cooling compensation
percentages by the thermal air-conditioning scenario, 30.8 % and 30.9 % for the Aswan-
TSFH and for the Aqaba-TSFH cases respectively.
2. The performance of the daily direct cooling compensation by the PV air-conditioning
scenarios is more efficient than in the thermal scenario although the flat plate collector
efficiency is around 50 % and the PV module is around 14 %, due to three reasons.
14 The cooling energy which covers the cooling demand when the air-conditioning system as without storage. 15 The cooling energy which covers the cooling demand only by the contribution of the storage in the air-conditioning system.
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The first and the main reason, the COP of the compressed chiller and the absorption
chiller are completely different. It is nearly 3 for the compressed chiller in the PV air-
conditioning scenario and it is around 0.7 for the absorption chiller in the thermal air-
conditioning scenario. The second reason, the solar flat plate collector starting to work
late in the morning and ended earlier in the evening. That is due to a low ambient air
temperature in the evening and in the morning times and the collector works at a high
temperature as 85 0C in order to drive the adsorption chiller. This makes the thermal
losses be higher than the solar gain from the flat plate collector which leads to
shutdown the device in these duration. The third reason, in the morning and at the
evening, there is electric power gain from the PV modules due to a high share of diffused
radiation and the ambient air temperature is lower than the noon’s. Hence a low
thermal effect on the PV module efficiency in these duration.
3. The percentage of the cooling energy compensation by the storage in the thermal air-
conditioning scenario is 20.1 % and 11.9 % for the Aswan-TSFH and for the Aqaba-
TSFH cases respectively. These are higher compared to those of PV air-conditioning
with storage scenario, 10.7 % and 7.3 % for Aswan-TSFH and Aqaba-TSFH respectively.
That’s because of the contribution of the e cess power which is produced by the flat
plate collector is higher than the excess output power of the PV module at noon. It can
be concluded that the PV air-conditioning with storage scenario needs less storage to
cover the same amount of cooling load demand compared to solar thermally air-
conditioning with storage scenario. In addition, the storage system in PV air-
conditioning scenario is minor and the direct compensation is major. That is vice versa
in the thermal air-conditioning scenario.
4. In winter season, the excess solar power gain is more useful in the PV air-
conditioning scenarios than the thermal air-conditioning scenario due to, the electric
power is more universal conversion compared with the thermal power conversion. The
excess electric power can be used for many other electric applications such as building
lighting or space heating etc.. The excess of the thermal heat power can be used only for
space heating or domestic hot water. In addition the excess electric power gain can be
fed to the grid if there is a feed-in-tariff in this region.
93
Comparison Between Aqaba-TSFH and Aswan-TSFH
The cooling demand follows the outside solar radiation and ambient air temperature
along the year due to solar gain through the building’s envelope. The monthly cooling
demand in Aswan-TSFH is higher than Aqaba–TSFH’s throughout the year e cept in
June, July and August although the solar radiation and the ambient air temperature in
Aswan city are higher than in the Aqaba city. Therefore, it is due to a higher ambient
relative humidity in Aqaba than in Aswan. This means ventilation increases the
humidity inside the building and results in a higher cooling demand in Aqaba-TSFH.
The contribution of the storage system (storage tank or battery system) to the cooling
energy compensation in each technology is more efficient in Aswan-TSFH case than in
Aqaba-TSFH case and it is almost double, because there is a higher solar radiation in
Aswan especially in summer season. This in turn means a better solar gain is stored
which can cover the night cooling demands.
The direct cooling compensation curve behaviour during the day of the PV air-
conditioning scenarios for the Aqaba-TSFH is better than the Aswan-TSFH. That’s due to
a higher diffusion and a reflected solar radiation which is observed in Aqaba city than in
Aswan city.
In the summer season, the cooling production by all scenarios in Aswan-TSFH case has
an excess of cooling production power at noon. But in the case of Aqaba-TSFH, the
situation is different: the cooling production rises up close to the maximum peak cooling
load demand. It can be concluded that the performance of the compensation cooling
load in the summer is optimized if the collector is tilted at 15° greater than the latitude
in each scenario in Aqaba-TSFH case. Then, more energy can be stored and used at
night.
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7.2 Future Research
In terms of energy efficiency in buildings and the feed-in-tariff law in Germany and in
Europe of self-consumption which becomes more important in these days, the
calculations of the TSFH cooling demand calculation and the cooling compensation of
each scenario based on the meteorological data with less than one hour or a 15 minute
time interval is necessary. In addition, it should be based on the real-time compensation
especially for the storage contribution.
One of the main objectives of the solar air-conditioning systems is to save primary
energy consumption, therefore the study can be extended to analyse and compare the
solar thermal air-conditioning scenario and the solar PV air-conditioning scenarios
under MENA regions’ climates in terms of primary energy and economic analysis.
Moreover, the future cost reduction by learning curves of both technologies can
influence the economic feasibility.
Further work should compare and analyse between the two technological scenarios in
the case of heat pump system in order to compensate the heating demand as well as the
cooling demand. Also, a comparison between these two technologies is necessary if
there is feed-in-tariff in the MENA region and the PV air-conditioning scenarios can use
the grid as storage.
The determination of the reference building (TSFH) in this study for the two locations
(Aswan, Aqaba) was based on the Jordanian TSFH envelope construction for both cases
under the assumption that there is no big difference between the Jordanian TSFH and
the Egyptian TSFH. Therefore, the Egyptian TSFH’s envelop constructions should also be
considered. In addition, this research can be extended to include different building
types such as office buildings.
95
References
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Technical and economic analysis on industrial refrigeration and air-conditioning
applications, Available online 20 February 2009, contents lists available at Science
Direct Website, www.sciencedirect.com.
[2] Nathan Rona, Solar Air-Conditioning Systems, Focus on components and their
working principles, Building Services Engineering, Department of Building Technology,
CHALMERS UNIVERSITY OF TECHNOLOGY, Göteborg, Sweden 5765/2004.
[3] Elsafty A , Al-Daini A.J, Economical comparison between a solar-powered vapour
absorption air-conditioning system and a vapour compression system in the Middle
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available at Science Direct Website, www.sciencedirect.com.
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