Air Conditioning System Performance of a City Hotel Appraised for Energy Use Efficiency

Abstract

This paper presents results of a study on the performance of split air conditioning (AC) and overall energy consumption of a city hotel in Bali, Indonesia. The study applied a practical global approach to appraising energy performance of the AC system, overall electrical energy consumption of the hotel and frequent compressor damage as the impact of installation methods of the existing AC systems. The results obtained indicate that improper AC system installation method can reduce their energy performance which include COP (coefficient of performance), EER (energy efficiency ratio), and SEI (system efficiency index). The finding also shows improper installation method can cause enormous compressor damage. Within three years, as many as 54 compressors from 90 existing AC system in a particular building were damaged. Overall number of compressors that have been faulty in that period can reach 76 units accounted for about 23.1% of the total AC systems installed in the hotel. It is also found there is a reduction on AC system cooling capacity.

Full text

Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 83, Issue 1 (2021) 118-139
118
Journal of Advanced Research in Fluid
Mechanics and Thermal Sciences
Journal homepage: www.akademiabaru.com/arfmts.html
ISSN: 2289-7879
Air Conditioning System Performance of a City Hotel Appraised for Energy
Use Efficiency
I Made Rasta1,*, I Nyoman Suamir1
1
Department of Mechanical Engineering, Politeknik Negeri Bali, Bukit Jimbaran, Kuta Selatan, Badung, Bali 80364, Indonesia
ARTICLE INFO
ABSTRACT
Article history:
Received
8 December 2020
Received in revised form
31 March 2021
Accepted
4 April 2021
Available online
26 May 2021
This paper presents results of a study on
the performance of
split air conditioning (AC)
and overall energy consumption
of a city hotel in Bali, Indonesia. The study applied
a
practical global approach to
appraising energy performance of the AC system
, overall
electrical energy consumption
of the hotel and frequent compressor damage as
the
impact of installation methods of the existing AC systems.
The
results obtained indicate
that improper AC system installation
method can
reduce their energy performance
which include COP (coefficient of performance), EER (energy efficiency ratio), and SEI
(system efficiency index). The finding also shows improper inst
allation
method can
cause enormous compressor damage
. Within three years, as many as 54
compressors
from 90 existing
AC system in a particular building were damaged.
Overall number of
compressors that have been
faulty in that period
can reach 76 units accounted for
about 23.1% of the total AC systems installed in the hotel. It is also found there is a
reduction on AC system cooling capacity
.
Keywords:
City hotel; AC system installation; AC
performance;
energy assessment
1. Introduction
Hotel is a unique commercial building equipped with various facilities. One of the hotel facilities
is air conditioning (AC) for the convenience of visitors. AC system has become the largest end user of
energy in the building sector. Improving building designs and optimization on the AC systems in order
to reduce cooling load and energy use is the subject of many researches in tropical climates. More
effort is required for developing countries to achieve low building cooling load and energy use, hence
building energy appraisals are becoming increasingly sophisticated.
Interestingly, urbanization, population growth, the increase of demand for comfort levels and
favorable thermal environment in buildings together with the increase in time spent indoors seem
to ensure that the trend of increasing energy demand in building sector will continue to increase in
the future [1]. Hotel is one of the commercial buildings that is unique among other buildings. The
hotel building has many areas with different facilities and diverse variability in the room that guests
expect. This leads to a different energy consumption compared to other buildings [2]. Buildings
* Corresponding author.
E-mail address: maderasta@pnb.ac.id
https://doi.org/10.37934/arfmts.83.1.118139

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account for the majority of energy consumption worldwide [3-5]. For industrialized countries, energy
consumption of buildings could range from 42 up to 45% [6-8].
Concerning the main parameter of building thermal performances used to measure AC systems,
specifically for city area, is related to the site-specific temperature. Therefore, accurate study of local
conditions is essential. The accuracy of building thermal performance simulations can be frequently
improved by paying attention to a phenomenon which is known as Urban Heat Island (UHI). This
phenomenon has a consequence of an increase in air temperature [9,10]. UHI affects energy
consumption of the buildings, which in turn affects the city environment [11]. Extensive literatures
discuss the UHI phenomenon can be found in the study by Zhou et al., [12] and Santamouris et al.,
[13] and its effects on building energy consumption have been reported in the study by Li et al., [14],
Palme et al., [15], and Lima et al., [16].
Energy-efficient retrofitting interventions and policies to reduce electricity consumption and
costs have been explored in many countries [17-21]. The interventions and policies include energy
efficiency for building envelopes and windows [22-25]. Energy consumption mainly comes from the
use of Heating, Ventilation and Air Conditioning (HVAC) systems [26,27]. Poor thermal performance
and low efficiency of HVAC systems of most buildings result in high energy consumption [28-29].
One method of reducing building energy consumption is through optimizing equipment
operation and control, like modification of set-point temperature which can be adapted to external
climatic conditions but maintains an acceptable level of comfort [30,31]. Using adaptive set-point
temperature can optimally reduce energy consumption in the building sector, mainly because of its
effect on HVAC system performance [32-34]. Modification of set-point temperature to higher level
actually provide the HVAC system to operate at higher evaporation temperature by which can
contribute to better energy performance [35,36]. Additionally, the use of a set-point temperature
appropriate to the environmental characteristics of each area can reduce energy consumption of the
building without implying a large economic investment [37].
AC system plays a very important role in maintaining indoor thermal comfort of the hotel,
especially for tropical and humid climates. In tropical climates, the energy consumed by HVAC system
can exceed 50% of the total energy consumption of a building [38]. Hence, there is tremendous
potential to improve the overall efficiency of AC system in buildings. One method of improving AC
system efficiency is through application of heat recovery to be integrated with the AC system [39]
and optimization of the heat recovery system by utilizing thermal energy storage [40]. Large amount
of energy use in hotel buildings contributes to high operational costs by 17-30% and significant
contribution to greenhouse gas emissions, global warming and climate change [41-43].
Initiatives for Nearly Zero Energy Buildings are increasingly important for tackling climate change
and reducing energy use [44,45]. Greater effort is required from the developer to achieve these
objectives, and energy appraisal is becoming increasingly sophisticated [46]. This study also involves
energy appraisal of a city hotel in Bali, Indonesia. The appraisal was conducted to building envelope,
AC system description including user practices, annual electricity consumption associated with
cooling zones. The appraisal also provides possibility to determine potential improvements in
reducing energy consumption [47,48]. By discovering energy saving potentials, it can help use energy
more efficiently in city hotel buildings and reduce CO2 emissions to the environment for sustainable
development.
The city hotel investigated in this study uses split type AC system. There are many factors found
to affect the AC performance which include set-point temperature, high temperature condensation,
low evaporation temperature, extremely hot compressor, noisy compressor, compressor stuck, and
very low degree of superheat refrigerant entering the compressor. The main problem appeared
which related to the function of AC system was that many compressors had started to be damaged

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since about two up to three years after the year of hotel opening. Though service life of split type AC
system in normal operating conditions is up to 15 years and service experts recommend users to
consider replacing split type AC system after every 10 years [49]. Problem related to energy
performance was also existed which could be determined from instant power measurement and
assessed from energy consumption of the hotel that was found to be far from the criteria of an
energy-efficient city hotel.
This paper presents performance evaluation on energy performance of split type AC applied for
a city hotel in Bali, Indonesia. Assessment on the AC performance including problems associated with
system functionality and energy performance due to AC system installation are also elaborated and
discussed. A very important finding about the impact of poor installation of the AC systems on
compressor life was also presented and discussed. This paper, additionally, proposes energy
efficiency improvement strategy and economic practices based on energy appraisal results and its
impact to electrical energy costs. It is also deeply discussed that by reducing level of energy
consumption of a city hotel, it can certainly provide a financial impact.
2. Materials and Methods
2.1 City Hotel Building Characteristic
The investigated city hotel is located in Denpasar city of Bali province, Indonesia. The hotel
comprises 4 buildings including 1 hotel building (Building-1) and 3 residence buildings (Buildings-2, 3,
and 4). The hotel building contains 90 guestrooms and convention center which a place for meetings,
incentive, convention, and exhibition consisting of 3 convention halls and 7 meeting rooms. Whereas
the residence buildings comprise 96 guestrooms which make the hotel have total guestrooms of 186.
As a city hotel, the entire floor area of the buildings is around 7842 m2. The hotel has been operating
since 2014.
2.2 Hotel Building Envelope
Facades of the Building-1 with 90 guestrooms and convention center face north and south. The
facades are considered to have a good design because they are facing to directions with relatively
low solar heat gain potential. Around the facades, the hotel environment is facilitated by a green
landscape with a variety of shady plants. The concept, which is also called a green landscape, can
provide a cooling effect on fresh air or infiltration air and in the end give a fairly low heat gain effect
on the guestroom load. Green landscape also provides cooling effect on the residence buildings. The
north, south facade and shading of the buildings can be seen in Figure 1.
Fig. 1. The north and south facades as well as internal
shading of the hotel buildings

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Figure 1 also shows façade-wall of the hotel buildings which uses glass-window with window and
wall ratio of less than 25%. The use of glass windows allows sunlight to penetrate inside the
guestrooms and can take advantage of daylight for the guest room lighting. Regarding the potential
heat gain through the glass, internal shading can reduce this consequence. In general, designers of
the hotel have succeeded in implementing environmentally friendly design to minimize heat gain
through the building envelope by placing the façades north and south and applying green landscape.
Internal shading can also minimize infiltration air and penetration of solar radiation into the
guestrooms.
2.3 Installed Air Conditioning System
2.3.1 Air conditioning system and installation
The hotel uses unitary type AC systems which can be grouped according to the building being
served. Building-1 uses concealed split type AC. The condensing units (outdoor) of the AC systems for
floors 3rd, 4th and 5th are installed on the roof of the building and for floors 1st and 2nd are installed
outside the building adjacent to the respective floors. Meanwhile, the indoor unit is a concealed type
placed above ceiling in front of bathroom. Each indoor unit is equipped with a blower, supply grill,
ducting from evaporator coil to supply grill and an air filter. The filter is used to clean air from the
room before it re-circulates to the evaporator coil. The AC system installed in each guestroom is
specified for cooling capacity of 9000 (Btu h-1). Installation of the outdoor units and the grill of indoor
unit can be seen in Figure 2. All AC systems in the hotel are still using refrigerant R-22.
Fig. 2. Split AC system applied for Building-1
In the Building-1, the indoor unit used is a concealed type with forced flow. This indoor type
chosen is quite uncommon. As a comparison, indoor of wall mounted type generally with induced
flow. The concealed type with forced flow has a disadvantage of having air back pressure due to air
burst into the evaporator coil. Back pressure causes the blower to require a higher static pressure
head than induced flow. If the blower specifications used are the same as the induced flow, it may
result in air flow shortage and it can be difficult to meet minimum flow requirements of the optimum
cooling effect. It can get worse if the evaporator coil is dirty. Another drawback of a forced flow
concealed type indoor construction which mounted above ceiling is that the difficulty of access to
evaporator coil for regular cleaning. The evaporator is blocked by ducting from the indoor to the
supply grill. Cleaning the evaporator coil is time consuming especially in preparing the access. For
cleaning the evaporator only, the guestroom cannot be sold for about three days. This is one reason
why cleaning the evaporator cannot be scheduled regularly by hotel management.
Buildings-2, 3 and 4 use wall mounted split type AC systems. Most of the indoor units are installed
at a higher position than the outdoor units. Only the AC systems for the 5th floor of each building are

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installed on the roof top with the outdoor position higher than the indoor unit. Typical installation of
the AC systems can be seen in Figure 3.
Fig. 3. Split AC system installed in residence buildings
The AC system capacities for residence buildings according to manufacturer specifications vary
from 6750, 9000, 13500 and 18000 (Btu h-1). AC system with 6750 (Btu h-1) cooling capacity installed
in Building-2, 3 and 4 are respectively as many as 70, 68 and 75 units. While the convention center
uses split type AC systems. The outdoor units of the AC systems are shown in Figure 4. The AC systems
used consist of split duct and split cassette types.
Fig. 4. The outdoor units of split AC systems for convention center
2.3.2 Ventilation system
The ventilation system is designed to maintain air quality so that it is comfortable and healthy.
The system controls intake of clean, pollutant-free and odorless fresh air into the guestrooms,
convention halls, meeting rooms, and offices with a certain amount according to the function of the
room. It maintains the O2 (oxygen) content at a sufficient level for guests or residents and prevent
level of CO2 (carbon dioxide) concentration above 1000 ppm (parts per million).
The ventilation system has not been integrated with the current AC system. Partial ventilation
can occur due to the presence of an exhaust fan in the toilet which can create negative pressure in
the toilet and also in the guestroom. This causes air in the corridor to enter the guestroom through
the door opening or when the door is opened. There is also a possibility that outside air can enter
from the window, although it is very small because the type of window is air tight (see Figure 1). The
window, however, is equipped with an open and close mechanism, so that guests can provisionally
open the window, especially when they require better ventilation. Relying on air from the corridor is
actually an inaccurate concept, because corridors are usually designed with negative pressure, with

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the intention that corridor air does not enter the guestrooms. For convention center, fresh air is only
obtained from infiltration through the doors. According to ANSI/ASHRAE Standard 62.1 [50], for
hotels: whether guest rooms, meeting rooms, convention halls or offices in order to obtain good air
quality, a minimum ventilation rate (minimum fresh air flow rate) of 2.5 LPS (liter per second) per
person is required. This is about 5 CFM (cubic feet per minute) per person.
Ventilation can result in additional cooling load from the AC systems and can also further increase
the operating costs. But in this modern era, operating costs can be reduced by reducing energy
consumption through the installation of an efficient AC systems and adequate maintenance. On the
other hand, the cost and quality of maintenance can also be affected by easy access to the AC
systems, so the selection of the AC system installation and the provision of access for maintenance
are also very important factors to consider.
2.4 Piping Installation and System Construction
The installation and construction methods of the split AC system in Building-1 can be divided into
2 groups, namely: (i) Group I: floors 1st and 2nd; (ii) Group II: floors 3rd, 4th and 5th. The AC systems in
Group I are the AC systems that have been reinstalled from an arrangement where the outdoor units
placed on the roof top of the building with elevation more than 15 m above the indoor unit to the
opposite arrangement where the outdoor units are installed with elevation below the indoor units.
This change was done after the hotel in operation for approximately 2 up to 3 years (2017). While
Group II comprises split AC systems with arrangement where the outdoor units installed on the roof
top of the Building-1 with elevation of about more than 10 m above the indoor units. Other buildings
were applied installation method as used in Group I of the Building-1.
Installation of outdoor units on the roof top of Building-1 and the piping system can be seen in
Figure 5. It can be clearly observed that the installation of the outdoor unit does not consider access
to maintenance and repair, nor space for ambient air circulation which could obstruct heat
dissipation from condensers.
Fig. 5. Condensing unit and piping installations of the hotel building
Installation of the refrigerant pipe for AC systems in Building-1 seems to have problems with the
length of the pipe which is far exceeding the length recommended by the manufacturer of 10 m
maximum for AC system of 9000 (Btu h-1) or lower cooling capacity. In addition, the installation
elevation between indoor and outdoor units by the manufacturer is usually limited to a maximum
elevation range from 5 m up to 7 m. The elevation difference, especially for cases where the outdoor
units are installed above the elevation of the indoor units, becomes very critical. Some issues on the
pipe insulation such as damaged insulation, discontinued insulation, pipe without insulation were
also found in the installation of AC system for Building-1.

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Pipe installation of the AC systems in Building-2, 3, and 4 (the Residence buildings) is relatively
better than that in Building-1. The installation of the outdoor units can be seen in Figure 6. In general,
the concept of outdoor installation from the side of cooling air circulation is very good, that is, it is
open and there are no walls or objects that block the flow of condenser air. In addition, almost all air
conditioners are installed by placing the indoor units at a higher elevation than the outdoor units,
except for the AC system for the 5th floor, the outdoor units are placed on the roof top of the
buildings. There are several aspects that need to be addressed by hotel management with regard to
AC systems in Building 2, 3 and 4, namely access to the outdoor units of the AC systems for
maintenance and repair. Some outdoor units are installed on walls that are difficult to access for
maintenance and repair. Other outdoor units have been installed with a proper approach to reach
the units for inspection and maintenance as shown in Figure 6.
Fig. 6. Outdoor unit installation of the AC system in residence
buildings
Installation of the AC system at the convention center seem to be considering access for
maintenance and repair. Additionally, the installation has placed the outdoor unit elevation below
the indoor unit. The outdoor unit installation of the AC systems is illustrated in Figure 4.
2.5 Methodology and Assumptions
Energy appraisal is one step in a comprehensive energy saving management and program related
to the AC (Air Conditioning) systems in hotel buildings. Without energy evaluation, it could be difficult
to measure system efficiency, performance and potential energy savings through system
optimization, modification and development. Evaluation of the impact of AC system installation
methods on energy performance of the AC system, overall electrical energy consumption of the hotel
and frequent compressor damage used primary data obtained from direct measurement and
secondary data gathered from hotel management together with data from site observation.
Internal method was applied for direct measurement in this appraisal. By using this method, it
provides possibility to thermodynamically develop refrigerating process and cycle of the AC system.
It can also offer a better assessment about system efficiency which based only on a short period and
instant measurement on site [51]. Parameters, that are necessary to be measured using this method,
include surface temperatures of the refrigeration system, refrigerant pressures and electric power.
Data and information required in this appraisal were gathered in two groups. Firstly, secondary data
was obtained from hotel management, hotel engineers as well as from manufacturer. Secondly,

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primary data was directly measured on the AC systems in field. Direct observation on the AC system
and other supporting facilities which include installation, operation, maintenance and repair has also
been performed to accomplish a comprehensive information and data required for the analyses. For
investigation purposes, a data logger system for measuring temperature and power consumption on
the AC system were installed and set up. To assist the investigation process, appraisal instruments
including digital and infra-red thermometers, digital air-flow meters, power analyzers, hot wire
temperature measuring instruments, thermocouples, and a digital camera were also used.
Fig. 7. Handheld instruments for automatic and manual measurements
The purpose of making direct measurements and observations is to obtain accurate data based
on actual operating conditions. Measurements were made using manual and automatic methods.
Operational data was recorded directly, automatically and continuously at the same time for various
parameters using a data logger (Figure 7(a)). Whereas the working pressure of the system, air flow
rate, surface temperature and relative humidity (RH) of the air were measured using manual
measurements (Figure 7(b)). Data obtained were recorded manually using handheld instruments.
Fig. 8. Schematic diagram of a split type AC system completed with site
measurement points for energy performance investigation

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Data obtained from measurements and observations were processed using spreadsheet and EES
(Engineering Equation Solver) programs. By using these programs, thermal properties of refrigerant
at various operating conditions can be retrieved and energy performance of the AC system can be
investigated and simulated. The programs were also used to estimate AC system performance under
different operational conditions.
Performance of the AC system was determined by using thermodynamic analysis on the
refrigeration cycle. Performance parameters used in the analysis were measured in every 30 seconds
for about 3 hours. Positions of the measurements are illustrated in a schematic diagram of the AC
system as shown in Figure 8. Measurements were randomly performed using 5 samples of AC
systems (two for Building-1 and one each for Building-2, 3 and 4).
Applying internal method, evaluation on the performance of the AC system which involves
cooling capacity (Qcool) and electric power consumption of the compressor (We,com) can be done
through temperature and pressure measurements in the refrigerant circuit. Temperatures and
pressures of refrigerant at various part of the AC system can be used to determine specific enthalpy
change of the refrigeration process in the system cycle. Cooling power or well-known as compressor
work rate (Ww,com) was estimated from heat loss to surrounding and electric power of the
compressor. For an AC system using hermetic compressor, the heat loss factor may be ranging from
3% up to 10% calculated from electric motor power and specifically for compressors operated at
normal ambient conditions, a fix value of 7% can be applied [51].
Assumptions were also taken to simplify the system evaluation which include: isenthalpic
expansion in the capillary tube, insignificant pressure drops in the heat exchangers and connecting
tubes, and 7% heat loss factor in the compressor. Refrigerant exiting the condenser is assumed to be
saturated liquid due to difficulty to installed pressure measurement on the high pressure side of the
existing system. There is no service valve at condenser side. To install a pressure measurement would
require modification of the tubing system and make the AC system unable to operate for hotel
services. This should be avoided in this appraisal. Based on these assumptions, refrigeration cycle of
the AC system used for analysis is illustrated in a pressure-enthalpy diagram as can be seen Figure 9.
Fig. 9. Refrigeration cycle of the AC system in
pressure-enthalpy diagram used for analyses

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Taking into consideration heat loss factor (fq), then compressor work rate (Ww,com in kW) can be
determined from Eq. (1).
comeqcomw
WfW
,,
)1( 
(kW) (1)
where We,com is electric power consumption of the compressor in kW. How far the compressor
deviates from an isentropic compression can be determined from isentropic efficiency which can be
calculated from Eq. (2).
%100
)(
)(
12
12
b
bs
s
hh hh


K
(%) (2)
where ηs = isentropic efficiency of the compressor (%); h = specific enthalpy of the refrigerant at
measuring points (kJ kg-1), corresponding subscripts refer to Figure 8 and Figure 9.
In this appraisal, one key parameter used as performance indicator of the AC system is COPm
(Coefficient of Performance; subscript m stands for measured) which expresses ratio of useful heat
or cooling capacity (Qcool in kW) over electric power consumption of the compressor (We,com in kW)
as formulated in Eq. (3).
come
cool
m
W
Q
COP
,
(3)
where Qcool can be determined from:
Qcool = ṁref (h1a – h4) (kW) (4)
b
comeq
b
comw
ref
hh
Wf
hh
W
m
12
,
12
,
)1(




(kg s
-1) (5)
where ṁref is refrigerant mass flowrate (kg s-1). Solving the Eq. (3)-(5), the COPm of the AC system
then can be also calculated by applying specific enthalpy changes of the compression process (in
compressor), heat absorption process in the evaporator together with compressor heat loss as shown
in Eq. (6). Subscripts in the equations refer to Figure 8 and Figure 9.
)(
)()1(
12
41
b
aq
m
hh
hhf
COP 

(6)
Others key performance indicators used of the AC system are EER (Energy Efficiency Ratio) and
SEI (System Energy Index). EER is a measure of efficiency correlated to COPm but its unit should be in
Btu h-1 W-1. Then, the EER of the AC system can be calculated from Eq. (7).
m
COPEER 412.3
come
cool
W
Q
EER
,
412.3
(Btu h-1 W-1) (7)

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SEI is also a measure of efficiency but it provides advantages compared to COPm. By using SEI,
system efficiency can be obtained at restricted field measurements. SEI is defined as the ratio of
calculated COPm over coefficient of performance of ideal process or the maximum theoretical COP at
desired operating conditions, which is also known as Carnot COP (COPC). SEI can be applied for
optimization of energy system and as a guide for selecting the main parts of an AC system. SEI and
COPC can be calculated from Eq. (8) and Eq. (9) respectively.
eva
evacon
b
aq
C
mTTT
hh
hhf
COP
COP
SEI )(
))(1(
12
41 


(8)
)(
evacon
eva
C
TT T
COP 
(9)
where fq = compressor heat loss factor; h = specific enthalpy of the refrigerant at measuring points
(kJ kg-1), relevant subscripts refer to Figure 8 and Figure 9; Teva and Tcon are evaporation and
condensation temperatures respectively (in Kelvin).
Energy performance of the AC system is directly related to the cooling load characteristics and
cooling capacity of the AC system and heat dissipation in the condenser unit. The mismatch between
building cooling demand, AC system cooling capacity and heat dissipation in the condenser can affect
the performance of the AC system. In order to comprehensively investigate the performance of the
AC system, the cooling demand of the hotel rooms was also estimated using the EES program. The
cooling demand estimation method is usually applied by combining the diversity factor based on the
cooling demand data analysis and how often each cooling demand element occurs. The diversity
factor also shows that all cooling demands do not occur at the same time and also not always at their
maximum value. For hotel buildings using unitary AC system, however, the diversity factor can be
assumed as a room peak load which is considered 100% of the calculated load [52].
The appraisal also involves energy consumption profile of the hotel which presented for two or
four years. Energy performance of the hotel has been identified by using Energy Use Intensity (EUI)
and Guest Energy Intensity (GEI). EUI is calculated from the ratio of energy consumption (kWh) over
floor area (m2) to be conditioned within a certain period of time (per month and per year). Whereas
GEI is a parameter that shows energy consumption (kWh) per number of guests staying (guest night)
and it is evaluated monthly.
3. Results and Discussion
3.1 AC System Energy Performance
Operational quantities required for AC system evaluation have been measured and recorded. Five
samples of AC systems were considered. The results of the measurement are given in Table 1. Data
presented are average values of every 30 seconds for 3 hours’ record. It can be seen the AC systems
of Group II (AC-1b) have worked with highest: compressor discharged temperature (T2),
condensation temperature (Tcon), evaporator degree of superheat and the lowest evaporation
temperature (Teva). The main cause this issue can occur is that the outdoor unit of the AC systems are
installed very closed to each other which can obstruct fresh air flow that cools the condenser. Dirty
evaporator can also cause the problems due to the indoor units are installed without proper access
for regular cleaning or maintenance. From the measurement data, it can also be identified there is
significant temperature gain for about 4 °C along the connecting pipe of indoor and outdoor units. It

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can increase further degree of superheat of the refrigerant entering the compressor which can also
lift discharge temperature (T2). Damaged insulation and pipe length much longer than specified by
manufacturer is very likely to be the cause. Other AC systems (AC-1a, AC-2, AC-3 and AC-4) are found
to have normal operational parameters.
Data obtained was processed using EES program. Energy performance of the AC systems were
thermodynamically determined and the results are shown in Table 2. Power consumption of the AC
systems was closed to their specifications. Their cooling capacity, however, varied from 8120 up to
9068 (Btu h-1). AC-1b was found to have the lowest cooling capacity. It was again due to dirty
evaporator because the indoor unit was installed without proper access for regular cleaning. Dirty
evaporator could cause weak air flow through the evaporator coil with an average air velocity coming
out of the inlet grill of 1.16 (m s-1) at high speed fan position. The air flow rate was found 0.125 (m3
s-1) or 264 (ft3 min-1). Normal airflow at maximum speed is specified for about 375 (ft3 min-1). This
resulted in the AC systems in Group II of Building-1 could not perform as good as other AC systems
with COPm 3.31 which accounted for about 6% lower than their specifications. Other AC systems were
found to perform as specified by their manufacturer with COPm range between 3.49 and 5.53.
Table 2 also contains AC systems compressor efficiency which was calculated from specific
enthalpy of ideal and actual compression processes based on system pressure and temperature
values using the internal method. EER and SEI of the AC systems are also presented. EER is correlated
to COPm and calculated from Eq. (7). While SEI has been determined from the ratio between COPm
and Carnot COP based on reference temperatures of condensation and evaporation at condenser
and evaporator side respectively.
Table 1
Measurement results of the operational quantities required for determining the AC system energy
performance
Measured quantities
Units
AC-1a
AC-1b
AC-2
AC-3
AC-4
Ambient temperature
Ԩ
30
31
30
30
30
Evaporation pressure (Peva),
Psi
70
69
70
71
72
with corresponding evaporation temperature (Teva)
Ԩ
5.0
4.6
5.0
5.4
5.7
Compressor inlet refrigerant temperature (T1b)
Ԩ
11.7
13.8
10.2
12.7
12.9
Compressor outlet refrigerant temperature (T2)
Ԩ
84
88.7
83.0
86.2
87.2
Temperature of refrigerant out evaporator (T1a)
Ԩ
11.5
9.8
10.2
12.7
12.9
Temperature of refrigerant out condenser (T3=Tcon)
Ԩ
47.1
48.6
47.2
48.1
48.4
Degree of superheat refrigerant at inlet compressor
K
6.7
8.8
5.2
7.7
7.2
Guestroom air temperature
Ԩ
26
25
26
25
25
Guestroom air RH
%
66
64
65
63
64
AC-1a = an AC system of Group I in Building-1; AC-1b = an AC system of Group II in Building-1; AC-2, 3 and 4 = AC
systems in Building-2, 3 and 4 respectively
Compressor efficiency of all AC systems are in a good range from 72.5% to 75.6%. Isentropic
efficiency of AC system’s compressor commonly ranges between 65% and 90%. With regard to EER
and SEI of the AC systems, it is found that the AC-1b, similar to its COPm, has the lowest EER of 11.28
(Btu h-1 W-1) and SEI of 51.9% which are accounted for 6.0% and 6.9% respectively lower than the
specifications. However, all evaluated AC systems are included in excellent SEI grade with SEI value
more than 40% as proposed by Lane et al., [51], which means the AC-1b also has excellent SEI. This
also confirms that in term of energy consumption, AC-1b is not the AC systems that has the highest
power consumption as shown in Table 2.
From these results, it can be summarized that the AC systems of the hotel buildings, in general,
still consume energy in the normal range. Even though energy performance parameters of some AC

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130
systems such as cooling capacity, COPm, EER, and SEI are found to be lower than the specifications.
However, the hotel management still faces some complaints especially for Building-1 that some
guestrooms are not cool enough. The analysis results have proven that the complaints are mainly
caused by some AC systems are not being able to provide sufficient cooling due to their low cooling
capacity. Even though their power consumptions remain in the normal range.
Table 2
Energy performance parameters of the AC systems simulated in EES program based on data
obtained from the field
Simulated parameters
Units
AC-1a
AC-1b
AC-2
AC-3
AC-4
Specified cooling capacity (name plate)
Btu h-1
9000
9000
9000
9000
9000
Specified power consumption (name plate)
kW
0.75
0.75
0.75
0.75
0.75
COP based on specified data
-
3.52
3.52
3.52
3.52
3.52
Isentropic efficiency of the compressor (ηs)
%
73.0
73.0
72.5
75.6
74.1
Compressor power (We,com)
kW
0.70
0.72
0.71
0.75
0.72
Compressor work rate (Ww,com)
kW
0.65
0.67
0.66
0.70
0.67
Calculated cooling capacity (Qcool)
kW
2.47
2.40
2.48
2.66
2.54
Btu h-1
8429
8120
8448
9068
8656
COPm
-
3.53
3.31
3.49
3.54
3.52
COPC
-
6.60
6.37
6.57
6.45
6.53
EER (Energy efficiency ratio)
Btu h-1
W
-1
12.04
11.28
11.90
12.09
12.02
SEI (System energy index)
%
53.5
51.9
53.1
55.0
53.9
3.2 Hotel Energy Profile
Appraisal on the hotel energy usage has shown that almost all energy needs for hotel service
facilities come from electrical energy. Monthly electrical energy consumption of the hotel is around
186 MWh and 168 MWh which is equivalent to electricity consumption of 2231 MWh and 2020 MWh
per year respectively for year 2018 and 2019. Monthly variation in electricity consumption of the
hotel for 2018 and 2019 can be seen in Figure 10.
Fig. 10. Variation of monthly energy use of the hotel 2018 and 2019
The electricity consumption correlates with hotel occupancy rates as one of the parameters that
can affect electricity consumption. Monthly occupancy variations for 2018 and 2019 are presented
in Figure 11. From Figure 10 and Figure 11, it can be seen that the relationship between energy
0
25
50
75
100
125
150
175
200
225
250
123456789101112
Energy consumption (MWh)
Months
2018 20 19

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consumption and occupancy rate appears to be irregular which means that the increase of occupancy
rate is not followed by the increase of energy use.
Fig. 11. Monthly occupancy rate of the hotel 2018 and 2019
In 2019, monthly and annual average occupancy rate was greater than 2018. However, the
electricity consumption in 2019 was lower than in 2018. This is due to the presence of another
parameter that can have a strong influence on electricity consumption, that is the usage of
convention center. In 2018, there were many events, meetings, seminars and conferences that were
intensive using convention center but most of the participants did not stay in the hotel. Convention
center is one of the hotel facilities with intensive use of electrical energy, specifically for AC systems
and lightings. Figure 10 and Figure 11 have illustrated that intensive use of the convention center can
boost overall energy use of the hotel even the guestroom occupancy rate decreases.
Fig. 12. Energy use intensity (EUI) of the hotel for two-year period
Furthermore, the energy performance parameters of the hotel are evaluated using EUI (Energy
Use Intensity), which is calculated based on the ratio of energy consumption (kWh) to the
conditioned floor area (m2) within a certain period of time per month or per year. The EUI monthly
variation of the hotel for 2018 and 2019 is illustrated in Figure 12. From the monthly EUI, it can then
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5 6 7 8 9 10 11 12
Hotel occupancy rate (%)
Months
2018 20 19
0
5
10
15
20
25
30
35
40
123456789101112
EUI (kWh m
-2.
month
-1
)
Months
2018 20 19

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be determined that the annual EUIs for year 2018 and 2019 are 284.48 and 257.61 (kWh m-2 year-1)
respectively.
Fig. 13. Guest energy intensity (GEI) for the year 2018 and 2019
Another parameter that is more appropriate to describe the energy performance of the hotel
industry without the need for a conditioned hotel building floor area is GEI (Guest Energy Intensity).
GEI is a parameter that shows energy consumption (kWh) per number of guests staying (guest night).
GEI monthly variations for 2018 and 2019 are presented in Figure 13. Annual GEI for 2018 and 2019
were obtained as low as 58.56 and 45.38 (kWh guest-1 night-1).
Fig. 14. Energy use intensity of the hotel from 2016 up to 2019
The change of EUI and GEI of the hotel from 2016 to 2019 are illustrated as shown in Figure 14
and Figure 15. From the figures, it can be seen that there was an increase in EUI and GEI
proportionally from 2016 to 2018, then a decrease in 2019. The increase in hotel energy consumption
from 2016 to 2018 was mainly due to an increase in occupancy rates and an increase in the number
of events at the convention center. However, the reduction of electricity consumption in 2019 was
mainly due to less intensive use of the convention center.
0
10
20
30
40
50
60
70
80
90
123456789101112
GEI (kWh guest
-1
day
-1
)
Months
2018 20 19
0
50
100
150
200
250
300
350
2016 2017 2018 2019
208.22
231.56
284.48
257.61
EUI (kW h m
-2
.year
-1
)
Yea rs

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Moving the outdoor unit position to a better elevation level for AC systems of Group I in Building-
1, which was conducted in 2017, did not have much effect on the decrease in energy consumption,
but provides cooling capacity improvements compared to cooling capacity in previous mounting
methods.
Fig. 15. Four-year guest energy intensity of the hotel
When compared with benchmarks as presented in Table 3 for GEI, the energy position or status
of the hotel can be described as follows: based on the GEI benchmark (Table 3), which is a parameter
commonly used for city hotels, the hotel is a hotel in the category of “High GEI rating” or “wasteful
energy” with an annual GEI is above 43 (kWh guest-1 night
-1) in the hotel class with number of
guestrooms falls in the range from 101 up to 200. Energy saving measures are urgently needed by
hotel management to lower energy consumption to a level that is not wasteful of energy.
Table 3
GEI benchmark for hotels [53]
GEI
Rating
Hotel size (number of guestrooms)
0-50
51-100
101-200
>200
High
118
87
43
50
Average
43
44
32
34
Low
12
18
25
22
GEI = Guest energy intensity (kWh guest-1 night-1)
3.3 Maintenance and Repair
The operation of a split AC system is relatively simple. In general, the operating system is
equipped with controls that regulate the operation of the AC system based on the attainment of
room air temperature. The controller automatically responds based on room air temperature and
turn off the outdoor unit. Guestroom air temperature can be adjusted through the control system.
Based on observations in the guestrooms, it is found that the AC setting has been setting at 18 °C.
This temperature setting is considered too low. According to several published studies, it shows that
room temperature settings can affect energy consumption of the AC system. Every 1 °C decrease in
room temperature setting can increase energy consumption by 3% until 6% [47].
Maintenance of the AC systems carried out by the engineering department of the hotel has been
well documented. For most of the AC systems, regular maintenance which includes cleaning
evaporator and condenser coils has been carried out regularly and scheduled every 3 to 6 months.
0
20
40
60
80
2016 2017 2018 2019
44.42
57.57 58. 56
45.38
GEI (kWh guest
-1
day
-1
)
Yea rs

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Repairs that carried out for every AC system have also been recorded. Repairs involve insufficient
refrigerant charge, water condensation on the refrigerant pipe surfaces and compressor
replacement.
Regarding the maintenance of indoor units of the AC systems in Building-1, the hotel
management confirmed that it was difficult to carry out maintenance due to poor access. It takes 2-
3 technicians and a minimum of three days to perform cleaning of the evaporator coil. This means
that during the maintenance process the guestrooms cannot be sold. Most of the time is spent for
establishing maintenance access to the evaporator coil. This indicates that regular maintenance
cannot be done regularly and consequently provides adverse effects that can decrease AC system
performance such as dirty evaporator, low load, ice blocking, water dripping from indoor units due
to melting ice blocking, and low cooling capacity. Additionally, the evaluation also showed that
selection and installation of indoor unit of AC systems in Building-1 did not consider maintenance
and repair aspects and results in very expensive and time-consuming regular maintenance.
3.4 Compressor Failure
The most worrying problem that occurs in the hotel is the early damage of the compressor in
relatively large and continuous quantities. The problem began to arise after the hotel operated
approximately 2 up to 3 years. Compressor damage usually begins with various symptoms, such as
no cooling effect, tripping overload relay, noisy compressor, and jammed compressor. The problem
intensively occurred on the AC systems installed in Building-1. In 2017 alone, there were 22
compressor replacements out of 90 AC units installed in Building-1 due to compressor faulty. This is
accounting for more than 24%. Detailed of compressor replacements are given in Table 4.
Table 4
Compressor replacement by year, building and floor
Building Name
2017
2018
2019
Total
Building-1(Hotel building)
Floor-1
4
2
4
10
Floor-2
4
3
4
11
Floor-3
6
8
2
16
Floor-4
5
2
3
10
Floor-5
3
2
2
7
Sub-total
22
17
15
54
Building-2 (Residence building)
Floor-1
0
1
1
2
Floor-5
0
0
2
2
Sub-total
0
1
3
4
Building-3 (Residence building)
Floor-1
0
4
0
4
Sub-total
0
4
0
4
Building-4 (Residence building)
Floor-1
0
0
1
1
Floor-2
0
3
5
8
Floor-5
0
0
1
1
Sub-total
0
3
6
9
Convention Center
0
1
0
1
Toilet and Office
0
0
4
4
Sub-total
0
1
4
5
Grand total
76

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Based on the compressor replacement data presented in Table 4 together with observation
results and maintenance records, it can be summarized that
i. Number of damaged compressors for AC systems in Building-1 is very high. More than 54
compressors out of 90 total existing AC systems have been damaged. It is about 60% of AC
systems have experienced compressor replacements;
ii. Compressor failure in Building-1 began to occur since 2017, whilst economic life of a
compressor or split AC system is 10 years (maximum 15 years) [49]. This means compressors
have been damaged far below their service life;
iii. Compressor damage in Buildings-2, 3, and 4 as well as convention center including offices also
occurred but it was relatively small compared to Building-1 with a ratio of 5-12% of the total
number of AC systems installed in each building. This occurred is mainly due to dirty
condenser especially for AC systems with poor access for maintenance as shown in Figure 6;
iv. Overall number of compressors that were damaged in the last 3 years were 76 out of 329 AC
systems or around 23.1%;
v. Installation of AC units in Building-1 is in principle different from AC system installation in
other buildings, specifically the elevation of the outdoor unit is higher than the elevation of
the indoor unit, with pipe lengths and elevation differences far exceed the manufacturer's
recommendations. This installation type adopted high suction pipe risers but without oil trap
at all. This inevitably prevents oil draining back to the compressor and leading to compressor
oil problems. Finally, it can damage the compressor. Additionally, excessive amount of oil
inside evaporator can reduce its cooling capacity.
Rearranging the outdoor unit position to a better elevation level for AC systems of Group I in
Building-1 has been conducted in 2017. The new arrangement includes the elevation of the outdoor
unit is lower than the elevation of the indoor unit. The pipe lengths and elevation differences are
within the manufacturer's recommendations. The new arrangement did not have much effect on the
decrease in energy consumption, but it can provide better cooling capacity and reduce compressor
damage compared to previous installation methods as illustrated in Table 4.
Significant number of damaged compressors is contrary to the recommendations of the ASHRAE
Handbook [54] which recommends that vapor compression AC systems are designed to avoid the
need for compressor replacement. The recommendation provides guidelines for selection and
installation of AC systems have to be properly designed in order to minimize the possibility of early
damage to the compressor.
Early compressor replacement certainly adds to the maintenance and repair costs of the AC
systems significantly because the budget of replacing a compressor can be as high as half the price
of a new split AC system. Therefore, a proper AC system selection and installation that are suitable
for building construction, cooling load demand and access for regular maintenance can ensure
excellent AC system performance and reduce energy consumption of the hotel as a whole system.
4. Conclusions
In this appraisal, assessing the energy performance of AC systems applied for a city hotel located
in Bali, Indonesia has been carried out. Related to energy performance of the AC system in the hotel,
it was found that there were several weaknesses in the installation and components selection of the
AC systems which include: (i) Some AC systems with their outdoor units installed on the rooftop of
the hotel building with very long pipe span and suction pipe risers far exceeding that recommended
by the manufacturer. The worse was the riser pipes were not equipped with oil trap. This inevitably
prevents oil back to the compressor and have damaged system compressors in three years of about

Journal of Advanced Research in Fluid Mechanics and Thermal Sciences
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54 (accounted for 60%) from 90 AC systems with the same method of installations. Most of the oil is
trapped in the evaporator itself. Excessive trapped oil in the evaporator can also influence heat
transfer and reduce cooling capacity of the AC system; (ii) Some AC systems were also found to have
their indoor units with poor access to carry out maintenance. This results in regular maintenance
cannot be done and consequently provides adverse effects that can decrease AC system
performance.
Energy performance of the AC system which finally affect the energy performance of the city
hotel can be summarized as follows: system efficiency index (SEI) of all evaluated AC systems in the
hotel are found to have excellent SEI grade with SEI values ranging from 51.9 to 55.0% which are
more than 40%. The results have also confirmed that in term of energy consumption, the AC systems
of the hotel buildings, in general, still consume energy in the normal range. However, they have lower
COP and lower cooling capacity than specified by manufacturer. Energy consumption profile of the
hotel in the last two years has also shown that energy status of the hotel, based on Gust Energy
Intensity (GEI), can be grouped in the hotels with “High GEI rating” or “wasteful energy” of annual
GEI is above 43 (kWh guest-1 night-1).
This assessment has shown that system selection, installation method and regular maintenance
have also a very important role on the AC system performance applied for city hotel. Opportunities
for energy efficiency improvement and saving electricity costs for the hotel can be improved through
modification of AC system installation and replacement of the improper AC system which is more
suitable to the hotel conditions and implementation of energy saving measures by hotel
management.
Acknowledgement
The research related to this article was supported by Politeknik Negeri Bali. The authors would like
to thank Politeknik Negeri Bali for administrative and financial supports.
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