Study on Power Consumption and Energy Performance of Split-Type Air-Conditioners

Abstract

An experimental study was carried out to compare energy performance of a non-inverter Air-Conditioner (AC) and that of an inverter AC having the same rated cooling capacity of 12000 BTU/h. Under different cooling part load values of 25%, 50%, 75%, and 91%, it is found that compared to the non-inverter AC, the inverter one can save from 10% to 52% of power consumption. Coefficient of performance (COP) of the inverter AC and that of the non-inverter one were also estimated to be in the range of 3.1 to 5.2 and 2.3 to 2.9, respectively.

Full text

Journal of Science & Technology 100 (2014) 031-035
31
Study on Power Consumption and Energy Performance
of Split-Type Air-Conditioners
Hoang-Luong PHAM1,*, Shogo TOKURA2 , Viet-Dung NGUYEN1,
Nguyen-An NGUYEN1, and Ngoc-Anh LAI1
1Hanoi University of Science and Technology, No. 1, Dai Co Viet Str., Hai Ba Trung, Ha Noi, Viet Nam
2Heat Pump and Thermal Storage Technology Center, Tokyo, Japan
Received: May 16, 2013; accepted: April 22, 2014
Abstract
An experimental study was carried out to compare energy performance of a non-inverter Air-Conditioner
(AC) and that of an inverter AC having the same rated cooling capacity of 12000 BTU/h. Under different
cooling part load values of 25%, 50%, 75%, and 91%, it is found that compared to the non-inverter AC, the
inverter one can save from 10% to 52% of power consumption. Coefficient of performance (COP) of the
inverter AC and that of the non-inverter one were also estimated to be in the range of 3.1 to 5.2 and 2.3 to
2.9, respectively.
Keywords: Split-type Air-conditioners, Power consumptions, COP, experimental study.
1. Introduction
Coefficient
*
of performance (COP) is normally
used to evaluate energy efficiency for AC, (Shao et
al., 2004; Zhu, 2006; Yu and Chan, 2007). Pham et al.
addressed that the COP of a 12000BTU/h inverter AC
consumes from 9.3% to 26.9% less electricity
compared to a non-inverter AC having the same rated
capacity (Pham et al., 2011a). Finally, Yokoyama
found that under part load condition, power
consumption of a 9000 BTU/h inverter AC is 8% to
10% lower than that of a non-inverter AC of the same
rated capacity (Yokoyama, 2011).
Based upon power consumption and COP
concepts, this study focuses on a comprehensive
comparison in energy performance of a non-inverter
AC and that of inverter-AC having the same rated
cooling capacity of 12000 BTU/h under Hanoi
climate conditions.
2. Experimental Set-Up and Calculation Method
2.1 Experimental set-up
The set-up used for this study consists of two
identical testing rooms each having a dimension of
4.9 m width, 3.0 m length and 3.2 m height, and
being insulated by polystyrene panels (Fig. 1). Major
details of the set-up were described elsewhere (Pham
et al., 2011a). For the current study, some
improvements were made i.e: i) Use of HF5 Rotronic
sensors with high accuracy for temperature and
*
Corresponding author: Tel (+844) 3868.0406,
Email: luong.phamhoang@hust.edu.vn
humidity measurement, ii) Better insulation and
sealing of the floor and ceiling of the testing rooms,
iii) Use of PLC controllers for artificial heat load
devices with different setting modes, and iv) Use of a
ceiling fans for better air circulation in the testing
rooms (Pham, et al., 2011b).
Before the experimental work was conducted,
a number of tests for heat transfer through the wall of
the rooms were conducted. Based upon the
experimental data, the heat transfer through the wall
of the rooms, Qloss, can be calculated as below.
For the room equipped with the inverter AC
Qloss= 41.554 (Toutside-Tinside) + 0.0289, W (1)
For the room equipped with the non-inverter AC
Qloss = 41.168(Toutside-Tinside) + 0.0338, W (2)
where Toutside and Tinside are outside and inside
temperatures of the rooms, respectively.
By setting the room temperature of 20 oC, the
air leakage of the room with the inverter AC and that
with the non-inverter AC were estimated to be 36 g
water per hour and 28 g water per hour, respectively.
These data show that the testing rooms are in good
airtight and insulation conditions.
2.2 Calculation of COP
COP of an AC in each testing room is defined
as: COP = Q0 / P (3)

Journal of Science & Technology 100 (2014) 031-035
32
Fig. 1. A schematic diagram of the experimental set-up.
Fig. 2. Effect of the outside temperature on power consumption of the inverter AC under part load ratios of
○ 91%, □ 75%,  50%, and  25% (-------), and that of the non-inverter AC under part load ratios of ● 91%,
■ 75%, ▲ 50%, and  25% ().
Where Q0 is the cooling capacity of AC which
equals to the sum of heat transferred through the wall
of the room, heat created by the circulation fan, and
heat generated by the artificial heat load device. P is
the power consumption by AC which is measured by
HIOKI measurement on an every minute interval.
Before each experimental run, the AC cooling load
can be fixed by keeping unchanged the inside
temperature of the rooms at around 27 oC and
controlling the electric power of the artificial heat
load device with a pulse width modulation method
(Pham et al., 2011a). AC part load ratio is ultimately
defined as ratio of the AC preset cooling load to its
rated cooling capacity.
3. Results and Discussions
3.1 Effect of the Outside Temperature on Power
Consumption of the AC
Table 1 presents the experimental results on
power consumptions of the inverter AC and that of
the non-inverter one under different cooling part load
ratios and at different outside temperatures measured
from July to September 2011. At each given
temperature, we average all measured values for the
cases having the given temperature plus and minus
0.5K. The relation between power consumption and
outside temperature under different cooling part load
ratios is shown in Fig. 2. As can be seen for both
cases of AC that: i) At a given part load ratio, the
higher the outside temperature, the higher the power
consumption of AC for both cases, and ii) At the
same outside temperature, the higher the part load
ratio, the higher the power consumption. These
observations do agree well with the theory.
0
200
400
600
800
1000
1200
28.0 29.0 30.0 31.0 32.0 33.0 34.0
Outside temperature (oC)
Power consumption (W)

Journal of Science & Technology 100 (2014) 031-035
33
Table 1. Power consumption of the two AC
Part load ratio
Toutside , oC
P inverter (1), W
P non-inverter (2), W
(1)-(2)
((1)-(2)) /(2)
25%
28
150
311
161
52%
30
170
321
151
47%
32
190
332
142
43%
34
210
342
132
39%
50%
28
312
570
258
45%
30
343
592
250
42%
32
373
614
241
39%
34
403
636
233
37%
75%
28
703
837
134
16%
30
757
887
129
15%
32
812
936
124
13%
34
866
986
120
12%
91%
28
1004
1115
111
10%
30
1018
1148
130
11%
32
1033
1181
148
13%
34
1047
1214
167
14%
Table 2. COP of the two AC
Part load ratio
Toutside (oC)
COP inverter (1)
COP non- inverter (2)
(1)-(2)
((1)-(2)) /(2)
25%
28
4.78
2.34
2.44
104%
30
4.72
2.50
2.22
89%
32
4.67
2.67
2.01
75%
34
4.62
2.83
1.79
63%
50%
28
5.17
2.85
2.32
82%
30
4.94
2.85
2.09
73%
32
4.71
2.86
1.85
65%
34
4.48
2.87
1.61
56%
75%
28
3.54
2.95
0.60
20%
30
3.43
2.89
0.55
19%
32
3.32
2.83
0.49
17%
34
3.22
2.77
0.44
16%
91%
28
3.10
2.85
0.25
9%
30
3.08
2.81
0.27
10%
32
3.07
2.78
0.29
11%
34
3.05
2.74
0.31
11%
Comparison in power consumption of the two
AC is illustrated in Fig. 3. From this Fig., one can
find that the higher part load ratio, the lower the
relative power consumption difference. Furthermore,
the lower the outside temperature, the more inclined
the relation between the relative power consumption
difference and part load ratios. It should be noticed
that this trend is different from that stated earlier by
Pham et al. (2011a). This could be intepreted that in
the previous work, the AC temperatures were fixed
while in this study, the rooms temperatures were kept
unchanged.
3.2 Effect of the Outside Temperature on COP of the
AC
Table 2 presents the experimental results on
COP of both non-inverter and inverter AC under
different part load ratios and at different outside

Journal of Science & Technology 100 (2014) 031-035
34
temperatures. Relative difference in COP of the non-
inverter and inverter ACs is also given in Table 2
which decreases quickly with an increase in the
outside temperature.
0%
10%
20%
30%
40%
50%
60%
0% 20% 40% 60% 80% 100%
Part load ratio (%)
(Pnoninverter-Pinverter)/Pnoninverter
Fig. 3. Effect of the part load ratio on relative power
consumption difference between the inverter and non-
inverter ACs at various outside temperatures of
○34 oC, □ 32 oC,  30 oC, and  28 oC.
Relation between the relative COP difference
and part load ratio at different outside temperatures is
presented in Fig. 4. The Fig. shows that the higher
part load ratio, the lower the relative COP difference.
Furthermore, the lower the outside temperature, the
more inclined the relation between the relative COP
difference and part load ratio. Again, this trend is
different from that obtained from the previous work
conducted by Pham et al., (2011a). The reason for
such difference is similar to that already addressed
when one examines the outside temperature on power
consumption of the AC.
0%
20%
40%
60%
80%
100%
120%
0% 20% 40% 60% 80% 100%
Part load ratio (%)
(COPinverter-COPnoninverter)/COPnoninverter
Fig. 4. Effect of the part load ratio on relative COP
difference of the non-inverter AC and inverter one at
various outside temperatures of ○ 34 oC, □ 32 oC,
 30 oC and  28 oC.
4. Conclusions
By carrying out an experimental study using
“two identical testing rooms” set-up with appropriate
improvements in room insulation, temperature
measurement and control, comparison in energy
performance of a non-inverter AC and an inverter AC
having the same rated cooling capacity of 12000
BTU/h was conducted.
Under part load ratios from 25% to 91% and
with outside temperatures variation from 28 oC to
34 oC, power consumption of inverter AC and non-
inverter AC is found to be from 150 W to 1047 W and
from 311 W to 1214 W, respectively. The power
consumption increases with an increase in part load
ratio and outside temperature. The relative power
consumption of non-inverter and inverter ACs is seen
to decrease from 52% down to 10% with increase in
part load ratio from 25% up to 91% that corresponds
with increase in outside temperature from 28 oC to
34 oC.
Under the same operating conditions, COP of
the non-inverter AC and inverter one was found to be
in the order of 2.3 to 2.9 and 3.1 to 5.2, respectively.
The relative difference in COP of the inverter and
non-inverter AC is observed to decrease from 104%
down to 9% with increase in part load ratio and with
increase in outside temperature difference. The results
obtained from this work have shown a suitable
application of inverter AC under Hanoi’s climate
conditions that would contribute to the reduction of
electricity consumption and thus CO2 emission from
the residential sector in Hanoi, Vietnam.
Acknowledgements
The authors gratefully acknowledge the Heat
Pump and Thermal Storage Technology Center of
Japan for their financial support for this study.
Laboratory facilities provided by the Hanoi
University of Science and Technology for this
research work are also highly appreciated.
References
[1] Pham H. L., Nguyen V. D., Nguyen N. A., Lai
N. A., Tokura S., Nakamura S., Development of
energy performance comparison method for
residential electric appliances – application to
air conditioners, Proceedings of the 10thIEA
Heat Pump Conference, Tokyo, Japan, pp. 13,
2011a.
[2] Pham H. L., Tokura S., Nguyen V. D., Nguyen
N. A., Lai N. A., Improvement of methodology
for energy performance estimate of small-scale
air conditioners in Vietnam, The First Project
Progress Report, submitted to the Heat Pump
and Thermal Storage Technology Center of
Japan, 2011b.
[3] Shao S, Shi W, Li X., Chen H., Performance
representation of variable-speed compressor for
inverter air conditioners based on experimental
data, International Journal of Refrigeration, Vol.

Journal of Science & Technology 100 (2014) 031-035
35
27 (2004) 805–815.
[4] Yokoyama K., Methodology for estimate of
Annual Performance Factor (APF) and its
application into Japanese Conditions,
Proceedings of the Vietnam-Japan Workshop on
Methodology for estimate of Annual
Performance Factor (APF) for Air Conditioners
in Vietnam, Hanoi University of Science and
Technology, Vietnam, 2011.
[5] Yu F.W., Chan K.T., Part load performance of
air-cooled centrifugal chillers with variable
speed condenser fan control, Building and
Environment, 42 (2007) 3816–3829.
[6] Zhu H., Impact of the Variable Refrigerant
Volume Air Conditioning System on Building
Energy Efficiency, HVAC Technologies for
Energy Efficiency, Proceedings of the 6th
International Conference for Enhanced Building
Operations, Shenzhen, China, Vol. IV-1-3, 2006