ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT
AZOJETE December 2019. Vol. 15(4):837-846

Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria.
Print ISSN: 1596-2490, Electronic ISSN: 2545-5818

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837

ORIGINAL RESEARCH ARTICLE

EVALUATION OF ENERGY CONSUMPTION AND CARBON DIOXIDE EMISSION FROM
A SOLAR / GAS POWERED ABSORPTION AIR CONDITIONING SYSTEM IN ZARIA

T. O. Ahmadu

(Department of Mechanical Engineering, Faculty of Engineering, Ahmadu Bello University, Zaria, Nigeria)
* Corresponding author’s email address: talibahmadu@gmail.com

1.0 Introduction
The energy demand for refrigeration and air conditioning has increased over the years
especially in developing countries. This is attributed to increasing need to prevent food spoilage
as well as increasing indoor comfort demands (Kalkan et al., 2012). Usually, electrically powered
vapour compression systems are used in refrigeration and air conditioning units. However, these
vapour compression systems consume high electric power, which leads to high electricity bills
(Henning, 2007). Also, these units operate with synthetic refrigerants such as hydro –
chlorofluorocarbons (HCFCs) which when released into the atmosphere constitute high ozone
depleting potential (ODP) (Sarbu and Sebarchievici, 2015). HCFCs are also known to exhibit high
global warming potential (GWP) of up to 2000 times that of carbon dioxide (CO2), which has a
GWP of 1 (Nair-Bedouelle et al., 2014). As agreed in the Montreal protocol, the schedule for the
phase out of production and consumption of HCFCs in developing nations is: 2015: reduction of
HCFC consumption by 10%, 2020: reduction of HCFC consumption by 35%, 2025: reduction of

ARTICLE INFORMATION ABSTRACT

Electrically powered vapour compression chillers consume high power
and make use of synthetic refrigerants which when released have
negative effect on the environment. In this study, the energy
consumption and carbon dioxide (CO2) emission from an absorption
air conditioning system were evaluated. The experimental scale
absorption air conditioning system has its thermal energy requirement
supplied by the solar collector system and liquefied petroleum gas.
The air conditioning system was operated for ten experimental days, in
both solar and gas heating modes. Daily power consumption by the
system was measured. The daily CO2 emitted by the system was
evaluated using the daily gas consumption. These were compared to
electric power consumption and CO2 emission from conventional
chillers of varying energy efficiency ratio (EER). Results showed that the
absorption cooling system has reduced power consumption in the
range of 31.5% to 64.2% as compared to conventional vapour
compression chiller of varying EER. Also, CO2 emission was seen to
have been reduced. This reduction was within the range of 13.3% to
43.2% when compared to that from conventional vapour compression
chiller of low to average EER.

© 2019 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved.

Submitted 14 September, 2018
Revised 21 January, 2019
Accepted 28 January, 2019

Keywords:
Absorption cooling
Energy
Carbon dioxide
Refrigerant
energy efficiency ratio

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Ahmadu: Evaluation of Energy Consumption and Carbon Dioxide Emission from a Solar / Gas Powered Absorption Air
Conditioning System in Zaria. AZOJETE, 15(4):837-846. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: talibahmadu@gmail.com 838

HCFC consumption by 67.5%, 2030: total phase out (Nair-Bedouelle et al., 2014). With the phase
out of HCFCs under the Montreal protocol on substances that deplete the ozone layer, the
introduction of alternatives with not only zero ODP but also low GWP and improved energy
efficiency is becoming an issue of increasing importance, especially in developing countries
(Nair-Bedouelle et al., 2014). Most vapour compression systems commonly use
chlorofluorocarbons (CFCs) and hydro – chlorofluorocarbons (HCFCs) refrigerants, which cause
depletion in the ozone layer. The replacements, which are hydrofluorocarbons (HFCs) have zero
ODP, but high GWP (Benhadid – Dib, 2012). A number of other available refrigerants that could
serve as replacements have properties that prevent them from being unconditionally adopted
(Nair-Bedouelle et al., 2014). Thermally driven absorption air conditioning systems have the
ability of working with low grade energy such as waste heat or solar energy. They consume low
electric power and have the ability to work with refrigerants with no harmful effect on the
environment, such as water (Henning, 2007). Water, when used as a refrigerant has zero ODP
(Benhadid – Dib, 2012). It is expected that the absorption air conditioning system can serve the
purpose of providing cooling with less harmful emissions to the environment and achieve high
energy efficiency. In this regard, several researchers have carried out works on absorption air
conditioning in recent years. Balghouthi et al., (2012) using a solar absorption air conditioning
facility of 16 kW capacity located in Tunisia, achieved solar fraction between 0.54 to 0.77. Also,
the facility was able to avoid CO2 of about 3000 kg from being emitted into the atmosphere
during the cooling season. Al – Alili et al. (2012), in Abu Dhabi, using a 10 kW NH3/H20 solar
absorption air conditioning system consumed 47% less electrical energy, with 12 metric tonnes/
year of CO2 emission reduction. Rosiek and Batlles (2012), in Spain, using a 70 kW absorption
chiller reduced the electricity consumption by 31% and led to a CO2 savings of 833kg. Sun et al.
(2015) experimented on a solar and gas fired absorption system for cooling and heating in
China. A 49.7% energy savings ratio was achieved. Zhai et al. (2015) experimented on a mini
type solar absorption air conditioning system of 8 kW capacity in China. The system was found
to consume 27% less power than a conventional chiller of same capacity. This study is aimed at
reducing the power consumption and CO2 emission associated with the use of conventional
vapour compression chillers, as well as experiment the use of water as refrigerant. This was
carried out by evaluating the power consumption as well as CO2 emission from an experimental
scale solar/ gas hybrid absorption air conditioning system of 3 kW cooling capacity, operating
under Zaria weather conditions. The power consumption and CO2 emission were compared to
those of conventional chiller of varying energy efficiency ratio (EER) which uses conventional
refrigerants.

2.0 Materials and Methods
Tests were conducted on an experimental scale solar/ gas hybrid powered absorption air
conditioning system, developed at the Department of Mechanical Engineering, Ahmadu Bello
University, Zaria, Nigeria.

2.1 Materials
The entire fabricated system consists of: An absorption chiller: This is of 3 kW cooling capacity,
which works on the lithium bromide water pair, where water serves as the refrigerant. A solar
collector: This uses solar radiation to generate the thermal energy required for the hot water. A

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gas burner: This is powered by liquefied petroleum gas and provides thermal energy required in
cases of low solar radiation. A storage tank: This is used to store the hot water. A wet cooling
tower: waste heat is rejected from the absorption chiller to the cooling tower. An indoor fan coil
unit: This is used to distribute cooled air to the test room.

The following instruments were used in taking measurements during the experiment:
i. Digital solar power meter: model no.: DBTU 1300, measuring range: 0 – 2000 W/m2,
accuracy: ± 5% of reading
ii. Digital thermocouple thermometer: model no.: T407291, measuring range: -50 – 1300°C,
accuracy: 0.1%+1°C
iv. Watt meter: model no.: H3680W, measuring range: 0 – 3680W, accuracy class: 1.0
v. Digital weighing scale: model no.: SF – 400, measuring range: 0 – 7000g, accuracy: ± 1g

2.2 Method
2.2.1 Experimental Procedure
Tests were conducted on selected days in the months of April and June 2017. Each day spanned
from 9:00 am to 5:30 pm. The experimental procedure employed is similar to that of Balghouthi
et al. (2012). Two heating modes were employed to provide the thermal energy required to
generate the hot water at the hot water tank: the solar power heating mode, provided via the
solar collector and the gas burner heating mode, provided by liquefied petroleum gas burner.
The hot water is required to desorb the refrigerant (water) from the lithium bromide solution in
the absorption chiller. At the start-up of each experimental day, thermal energy was supplied to
the water in the tank using the gas burner. This was because solar radiation is usually very low
at the early hours of the day to attain heating to required water temperature. When the
required temperature in the tank was attained (90°C – 99°C), the hot water pump was then
turned on to circulate the hot water between the tank and the absorption chiller. When the
temperature of the collector fluid increased to 80°C and above, the gas burner was disengaged,
and the system was switched to solar heating mode. When temperature of the collector fluid
drops below 80°C, the system was switched back to gas burner heating mode. Chilled water was
produced at the evaporator in the absorption chiller and pumped using the chilled water pump
to the fan coil unit in the test room which covers a total floor area of 9.21m2. Heat generated at
the absorption chiller was rejected to the cooling tower. Temperature readings were taken every
fifteen minutes from sensors attached to the system components and test room. Solar power
was measured using a solar meter. Gas consumed was measured by placing the gas burner on a
weighing scale and taking measurements as a result of weight loss at intervals. Power
consumption by the absorption chiller was measured using a Watt meter. Figure 1 shows a
schematic of the experimental set up.

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Ahmadu: Evaluation of Energy Consumption and Carbon Dioxide Emission from a Solar / Gas Powered Absorption Air
Conditioning System in Zaria. AZOJETE, 15(4):837-846. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: talibahmadu@gmail.com 840

Figure 1: Schematic of the experimental set up

The experimental days in which the experiments were conducted were chosen so as to reflect
varying weather conditions. This was done so as to test the performance of the system under
varying weather conditions. Accordingly, the experimental days were classified as follows:
Hot clear sky day: days with very clear sky, high solar radiation, no rain.
Fairly clear sky day: days with intermittently clear sky and partly cloudy sky, average solar
radiation, no rain.
Cloudy sky day: days with very cloudy sky, low solar radiation, no rain.
Rainy day: days in which rain occurred within any interval of the experimental day.

Figures 2 and 3 show components of the experimental absorption air conditioning system and
section of the absorption chiller respectively.

Figure 2: Outdoor components: Solar collector, Figure 3: Section of the absorption chiller
Hot water tank, gas burner, cooling tower

2.2.2 Evaluating solar fraction
The solar fraction was calculated as a ratio of the number of hours of the day in which the
system was powered in the solar heating mode to the total hours of operation of the day.

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2.2.3 Measuring gas consumption
The weight of gas consumed at an interval of time was determined by weight difference over
the time interval using a digital weighing scale. The gas consumption in kW(Pgas) was computed
using equation 1 as:

Pgas =
mCalg
t

(1)

where:
m is the weight of the gas consumed in the time interval (kg)
Calg is the calorific value of liquefied petroleum gas taken as 46.1MJ/kg (Demirel, 2012)
t is the time interval (seconds) for which the gas was used.
The gas consumption in kWh was obtained by multiplying the gas consumed in kW by the
period in which the system was operated in gas burner heating mode (hours).

2.2.4 Evaluating CO2 emission
According to Balghouthi et al., (2012), 680g of CO2 are emitted into the atmosphere for every
kWh of electricity produced by fossil fuel fired power plant. That is 0.68 kg CO2 emitted/kWh
electricity produced. Also 0.2 kg of CO2 is emitted into the atmosphere for every kWh of LPG
gas consumed. That is 0.2 kg CO2 emitted/kWh LPG gas consumed.
The mass of CO2 emitted to the atmosphere on using conventional chiller was computed
according to Balghouthi et al., (2012) using equation 2 as:

CO2(c) = power consumed(c) kW × hours of operation h × no. of days × fe( kg kWh) (2)

The mass of CO2 emitted to the atmosphere on using the experimental absorption cooling plant
was computed using equation 3 as:
CO2(a) = power consumed(a) kW × hours of operation h × no. of days × fe kg kWh +
(fg kg kWh × gas consumed kWh ) (3)
where:
fe is a conversion factor for CO2 emitted using fossil fuel (0.68 kg CO2/kWh)
fg is a conversion factor for CO2 emitted burning LPG gas (0.2 kg CO2/kWh)
power consumed a (kW) is the measured power consumption of the absorption cooling plant
which was 0.5 kW. This comprises the power consumption of the pumps and fan.
power consumed c (kW) is the power consumption by conventional vapour compression chiller
of varying energy efficiency ratio (EER), calculated using Equation 4:

power consumedc(kW) =
Cooling output

EER
(4)

The energy efficiency ratio (EER) is the ratio of cooling output from the chiller to the power
consumed by the chiller. Average allowable EER specifications for conventional vapour
compression chillers manufactured in different countries according to Phadke et al. (2014), was
used. Consequently, the power consumption for conventional vapour compression chillers

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Ahmadu: Evaluation of Energy Consumption and Carbon Dioxide Emission from a Solar / Gas Powered Absorption Air
Conditioning System in Zaria. AZOJETE, 15(4):837-846. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: talibahmadu@gmail.com 842

resulting from the different EERs was computed for a 3 kW cooling capacity chiller using
Equation 4.
For the whole experimental days, the absorption cooling plant was able to achieve an average
cooling power of 1.5 kW, while an average space cooling temperature of 24°C was attained.

2.2.5 Electric power consumed by the absorption cooling system (kWh)
This was obtained by multiplying the power consumed by the absorption cooling system (kW)
by the hours of operation (h). The system was operated for eight hours in each of the
experimental days.

3. Results and Discussion
In this section, results from the evaluation of energy consumption and CO2 emission by the
absorption cooling system are presented. Comparison is made between the absorption system
and conventional vapour compression system in terms of energy consumption and CO2
emission.
Following the classification of the experimental days done in section 2.2.1, accordingly, the days
were classified as follows:
Hot clear sky: April 22, June 6, 2017
Faily clear sky: June 3, June 8, 2017
Cloudy sky: June 12, June 18, June 19, 2017
Rainy day: June 7, June 13, June 17, 2017
Table 1 shows the average solar radiation, solar fraction and hours of electricity consumption for
the experimental days.

Table 1: Average solar radiation, solar fraction and hours of electicity consumption for
Experimental Days

Apr-22 Jun-03 Jun-06 Jun-07 Jun-08 Jun-12 Jun-13 Jun-17 Jun-18 Jun-19
Av. Solar
radiation
(W/m2) 967 751 918 95 785 574 206 158 568 513
Solar fraction 0.6 0.34 0.51 0 0.27 0 0 0 0 0
Hours of
electricity
consumption 8 8 8 3 8 8 5 4 8 8

The solar fraction is the fraction of thermal energy requirement for the day that was supplied by
the solar collector. From Table 1, it can be observed that the days of April 22 and June 6 which
were classified as hot clear sky days recorded average solar fractions above 900 W/m2. This
resulted in the relatively higher solar fractions of 0.6 and 0.51 recorded respectively on these
days. Solar fractions of 0.34 and 0.27 were also recorded on June 3 and 8 respectively, which
were classified as fairly clear sky days. The other days recorded no solar fraction as a result of
the very cloudy or rainy nature of the days. From the Table, it can be seen that the hours of

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electricity consumption for five of the experimental days is eight hours. However, the days of
June 7, 13 and 17 which were classified as rainy days all have lower hours of electricity
consumption. This is because, during the hours in which the rain lasted, there was no cooling
demand from the test room as the room was naturally cooled. The chiller was therefore shut
down during these hours, thus there was no electricity consumption.

Figure 4 shows the energy consumption for the experimental days. It can be observed that the
electricity consumption was regular at 4.0 kWh for the experimental days, except for the rainy
days of June 7, 13 and 17 which had lower electricity consumption. This was because the chiller
was run for fewer hours on the rainy days as seen earlier from table 1. Also, the gas
consumption can be seen to be lowest at 4.09 kWh on April 22. This was due to the high solar
radiation which resulted in high solar fraction, as seen earlier from Table 1. The cloudy days of
June 12, 18 and 19 can be observed to have the highest gas consumption of 12.3 kWh. This was
because the solar radiation was too low and the system thermal energy had to be provided by
the gas burner throughout these days.

Figure 4: Energy consumption of the absorption chiller for the experimental days

Figure 5 shows the CO2 emitted from the absorption cooling system for the experimental days.
From the figure, it can be observed that the rainy days of June 7, 13 and 17 had the lowest CO2
emissions of 2.07, 3.4 and 2.5 kg respectively. This was because the system was run for fewer
hours on gas burner mode in these days. Also, the electricity consumption on these days was
very low, thereby reducing the electricity component of CO2 emission. The hot clear sky days of
April 22 and June 6 also recorded relatively low CO2 emissions of 3.5 and 3.7 kg respectively.
This was due to high solar radiation availability which resulted in lower gas consumption. The
cloudy sky days of June 12, 18 and 19 recorded the highest CO2 emissions of 5.1 kg each. This
was because gas was consumed throughout these days to provide the required thermal energy.

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Ahmadu: Evaluation of Energy Consumption and Carbon Dioxide Emission from a Solar / Gas Powered Absorption Air
Conditioning System in Zaria. AZOJETE, 15(4):837-846. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: talibahmadu@gmail.com 844

Figure 5: CO2 emitted by the absorption cooling system for the experimental days.

Figure 6 compares the power consumption by the absorption cooling system with the power
consumption by conventional vapour compression chillers of varying EER. From the Figure it is
observed that the absorption system consumes power of 0.5 kW. This is much lower than the
power consumed by the conventional chillers shown in the figure. While the chiller with EER of
2.14 consumes 1.4 kW, the chiller with EER of 3.16 consumes 0.9 kW and the chiller with EER of
4.1 consumes 0.73 kW. This implies the absorption cooling system has reduced power
consumption in the range of 31.5% to 64.2% as compared to conventional vapour compression
chiller of varying EER. Similar reduction in power consumption by absorption cooling system
have been reported in the works of Alili et al. (2012) and Zhai et al. (2015).

Figure 6: Comparison of power consumption by the absorption cooling system with that
consumed by conventional vapour compression chiller of varying EER

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Figure 7 compares the CO2 emissions from the absorption cooling system with the CO2
emissions from conventional vapour compression chiller of varying EER for the ten experimental
days. It is seen that the absorption cooling system had a total CO2 emission of 38.6 kg for the
ten experimental days. This is observed to be lower than the CO2 emissions from corresponding
number of days from the chillers with low to average EER of 2.14, 2.75 2.92 and 3.16, which had
CO2 emissions of 68 kg, 53 kg, 50 kg and 44.5 kg respectively. It is observed to have about the
same CO2 emission with the chiller of high EER of 3.7 which had CO2 emission of 39 kg. The CO2
emission from the absorption chiller was however higher than that from the chiller with very
high EER of 4.1, which had CO2 emission of 36 kg. This could be attributed to the high gas
consumption especially on cloudy days. This implies the absorption cooling system has CO2
emission reduction within the range of 13.3% to 43.2% when compared to CO2 emission from
conventional vapour compression chiller of low to average EER. This is in agreement with CO2
emission reduction by absorption cooling system as reported in the works of Balghouthi et al.
(2012) and Rosiek and Batlles (2012). However, it has about the same CO2 emission when
compared to conventional vapour compression chiller with high EER. While the CO2 emission
from the absorption cooling system is higher than that from conventional vapour compression
chiller of very high EER by 7.2%.

Figure 7: Comparison of CO2 emission by absorption cooling system to CO2 emission by
conventional chiller of varying EERs

4. Conclusion
Electric power consumption, gas consumption and CO2 emission from a solar/ gas powered
absorption air conditioning system has been evaluated. Results from the ten experimental days
showed the least gas consumption occurred on days with high solar fraction while the highest
gas consumption occurred on days with very low or zero solar fraction. The absorption cooling
system had reduced power consumption in the range of 31.5% to 64.2% as compared to
conventional vapour compression chiller of varying EER. Also, CO2 emission reduction within the
range of 13.3% to 43.2% when compared to CO2 emission from conventional vapour
compression chiller of low to average EER were seen. CO2 emission from the system was not
significantly lower when compared to conventional vapour compression chiller with high EER
and becomes higher when compared to that from chiller with very high EER. This implies the

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Ahmadu: Evaluation of Energy Consumption and Carbon Dioxide Emission from a Solar / Gas Powered Absorption Air
Conditioning System in Zaria. AZOJETE, 15(4):837-846. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: talibahmadu@gmail.com 846

absorption cooling system offers the possibility of reduced electricity consumption, however,
improvements to bring about reduced gas consumption which translates to further reduction in
CO2 emission are required.
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http://www.cseindia.org
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