This paper was published in the International District Energy Association (IDEA) magazine 4th quarter 2015. The article describes the planning philosophy, design challenges and evaluation of performance of the system.

1. District Energy / Fourth Quarter 2015 7© 2015 International District Energy Association. ALL RIGHTS RESERVED.
FEATUREFEATURE Putrajaya Core Island Plant 4:
Malaysia’s first remotely charged chilled-water
storage system
Arul Hisham Abdul Rahim, Principal, AHAR Consultants; and
Rosli Mohamed, Partner, AHAR Consultants
S
ince 1999, Malaysia has had
a new federal administrative
center: Putrajaya, a 5,000-acre
planned city that is one of
Southeast Asia’s largest construction
projects. Still in development some
15 miles south of Kuala Lumpur, it
was established as part of the Malay-
sian government’s plan to move its
agencies and ministries out of “KL”
to alleviate traffic congestion and
preserve that city’s status as a major
commercial and financial hub.
Putrajaya is gearing up to one day
accommodate a resident population
of 350,000; it currently has around
72,000 inhabitants. The federal, com-
mercial and residential buildings
rising up across the city stand amid
lush green parks, botanical gardens,
wetlands and a 1,600-acre manmade
lake – forming a landscape that
planners have called an “intelligent
garden city.” Putrajaya is divided
into 20 “precincts,” with a concentra-
tion of employment and commercial
development in the four precincts on
Putrajaya Core Island.
Gas District Cooling (Putrajaya)
Sdn Bhd (GDCP) supplies the chilled
water to air condition approximately
13 million sq ft of space in Putrajaya.
The company is a subsidiary of Malay-
sia’s largest district cooling provider,
Gas District Cooling (M) Sdn Bhd (part
of the PETRONAS group of compa-
nies), which currently owns, manages
and operates six cogeneration/district
cooling plants in Putrajaya.
GDCP’s newest district cooling
facility in the city, Plant 4, was com-
pleted in early 2013 on Putrajaya Core
Island. It was built in anticipation of
new office buildings in the island’s
Precincts 3 and 4. GDCP sought the
optimal solution to accommodate the
corresponding expected increase in
cooling demand – and the result was
a chilled-water storage system that is
the first of its kind in Malaysia.
PLANNING FOR THE FUTURE
Putrajaya was conceived to be
an integrated development that
would take into consideration all
the administrative and technology
needs of its residents and tenants.
The infrastructure services – elec-
trical, domestic water, telecom-
munications and chilled water – for
buildings in Precincts 2, 3 and 4 on
Putrajaya Core Island are connected
through the Putrajaya Combined
Utility Tunnel along the island’s
main boulevard.
The Seri Gemilang Bridge, a Putrajaya landmark, serves as the main entrance to the Core Island from the south.
Courtesy © CEphoto, Uwe Aranas/CC-BY-SA-3.0.
GDCP’s Plant 4, commissioned in March 2013,
includes a 100,000-ton-hr thermal energy
storage system that utilizes chilled water
produced during off-peak periods at Plant 2.
Courtesy AHAR Consultants.

2. 8 District Energy / Fourth Quarter 2015 © 2015 International District Energy Association. ALL RIGHTS RESERVED.
In most commercial and govern-
ment offices in Malaysia, air condi-
tioning accounts for more than
60 percent of total building energy
use. Prior to the completion of Plant
4, the island’s Precinct 2, 3 and 4
building air-conditioning needs were
served solely by GDCP Plant 2, located
at Precinct 2. Built in 1998, Plant 2 is
a cogeneration facility utilizing natu-
ral gas to provide energy for steam
absorption chillers, direct-fired chill-
ers and electricity generation for its
own use. The plant is also connected
to the grid of Tenaga Nasional Berhad
(TNB), Malaysia’s national electric
utility, for access to standby and top-
up (peaking) power when needed.
In 2009, the city’s master develop-
er Putrajaya Holdings Sdn Bhd under-
took a strategic planning study of the
future chilled-water supply needed to
meet the cooling needs of Core Island
buildings. At the time, the cooling
demand from Precinct 3 and 4 build-
ings was anticipated to exceed the
generating capacity of Plant 2 by 2013.
As the city’s buildings are mainly
offices, 95 percent of the cooling load
occurs during the day. Due to this,
Plant 2 equipment had to be turned
on and off daily depending on the load
demand. This imposed operational
stresses on the equipment, especially
the gas turbines, shortening their life
expectancy. In addition, the Plant 2
site was already fully developed and
could not be expanded further.
THE COOLING DEMAND FROM
PRECINCT 3 AND 4 BUILDINGS
WAS ANTICIPATED TO EXCEED
THE GENERATING CAPACITY OF
PLANT 2 BY 2013.
Installing a new chiller plant
could address the need for additional
new cooling load demand. However,
the energy cost would also increase
correspondingly: With the price of
gas, electricity and water expected to
rise in the future, the generating cost
for chilled-water supply would also
go up. Another option studied was
reducing peak cooling load demand
by load shedding through the use of
chilled-water thermal energy storage.
It is very well-documented world-
wide that the installation and use of
chilled-water storage is an effective
way to meet cooling load and at the
same time lower energy cost (and
often also decrease capital cost).
The maximum sendout capac-
ity from the existing GDCP Plant 2
and two potential locations for a new
plant (plots 4U1 and 4U2) were evalu-
ated. Figure 1 shows the existing and
potential future distribution piping
and plants as studied in 2009. It was
decided that construction of a new
plant at plot 4U1 (Plant 5) was not
feasible because of the high capital
cost, which would have included the
installation of new plant equipment
and a new chilled-water pipe loop.
Plant 2, designed to primarily
serve Precinct 2, had been extended
to provide cooling energy to Precinct
3 and Precinct 4 between 2007 and
Figure 1. GDCP Existing and Potential Future Plant Locations and Piping on Putrajaya
Core Island, 2009.
Source: Gas District Cooling (Putrajaya) Sdn Bhd.
ST10
ST9
ST8
ST7
ST20
BRIDGE6
BRIDGE4
BRIDGE9
BRIDGE8
PUTRABRIDGE
PRECINCT 4
PRECINCT 3
PRECINCT 2
DATARAN
DATARAN
WAWASAN
DATARAN
PUTRAJAYA
RAKYAT
KHAZANAH
DATARAN
PROMENADE
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4R9
4R84R7
4R6
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3C5
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18P8
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2U6
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4T3
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TRANS
LOCAL
CEMENT RENDER
PAVER
DOTTED LINE TO SHOW WALL
CEMENT RENDER
CEMENT RENDERCAPACITOR CEMENT RENDER
CEMENT RENDER
CAPACITOR
( 50 TONNE )TRANSFORMER
2
N.E.R
PPU
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GASMALAYSIA
DISTRICTMETERING
GDCCONSUMER
GASMETERINGSTATION
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CEMENT RENDER( 50 TONNE )TRANSFORMER
2
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STATION
PLOT 2U1
PLANT 2
PLOT 4U2
PLANT 4
PLOT 4U1
PLANT 5
N
S
EW
Existing Chilled-Water Piping
Potential Future Chilled-Water Piping

3. District Energy / Fourth Quarter 2015 9© 2015 International District Energy Association. ALL RIGHTS RESERVED.
2009, in order to cater to the new
development at the middle and
southern end of Core Island. Plant 2
chilled-water production consisted
(and still consists) of a series of steam
absorption chillers, direct-fired chill-
ers and electric centrifugal chillers.
It also produced (and continues to
produce) around 9 MW electricity for
its ancillary equipment and approxi-
mately 24,000 tons of maximum cool-
ing capacity after taking into consid-
eration equipment degradation and
standby capacity.
In light of the remote locations of
some prospective development plots,
particularly those located at the Core
Island’s southernmost tip, the site for
Plant 4 was chosen because of its
·· close proximity to existing cooling
load demand and near-term
customers;
·· reasonable proximity to existing
Plant 2, which would make remote
thermal energy storage tank
charging from Plant 2 a possibility;
and
·· availability of existing utilities
infrastructure (electricity, water,
chilled-water pipes and gas).
With a charging capacity at Plant
2 of 20,000 tons operating for 10 hours
a day, it was theoretically possible to
produce up to 200,000 ton-hr for stor-
age. Chilled-water generation by Plant
2 with thermal energy storage at Plant
4 was determined to be able to serve
all existing and under-construction
loads during daytime peak periods.
TYPICAL LOAD PROFILE
In a typical day in 2009, the
peak load at Plant 2 (fig. 2) occurred
between 6 a.m. and 9 a.m. when the
plant experienced pulldown load from
the buildings. From 10 a.m. on, the
load profile was relatively constant
until 5 p.m. when the offices were
closed. Based on the foregoing, the
following conclusions were derived:
1. Plant peak load was approximately
25 percent of the average plant
sendout load.
2. The coincident building peak loads
of 20,000 tons occurred during this
same 6-9 a.m. period due to the
similarity of building type (i.e., pri-
marily office buildings).
3. Demand-side management such as
precooling of the buildings during
nighttime was not practiced by the
buildings’ operators to reduce this
peaking pulldown load demand.
4. The buildings’ load profile of around
16,000 tons was generally quite con-
stant from 10 a.m. until 5 p.m.
5. There was hardly any night load.
6. In addition to the anticipated
higher cooling load demand in the
future, higher peaking load occur-
ring early in the morning also
necessitated that more chillers be
run to meet the cooling load.
PLANT 4 DESIGN GOALS
The capacity and options study
was completed at the end of 2009.
Subsequently, the design team, led
by AHAR Consultants together with
the architect, cost surveyor, civil and
structural engineers, proceeded with
the design and construction of Plant
4. The design goals for Plant 4 were to
·· accommodate the increase in new
customers’ chilled-water demand;
·· optimize asset utilization of Plant 2;
·· increase Plant 2 in-house electricity
generation efficiency and reduce
electricity import from TNB;
·· reduce frequent start-stop opera-
tion of gas turbines at Plant 2,
improving their life span;
·· mitigate the peaking load while
using the existing chillers at Plant 2;
and
·· provide better control of chilled-
water supply temperature.
Plant 4 was designed as a hybrid
plant consisting of chilled-water stor-
age and electric-driven chillers. The
construction of the whole plant was
phased as follows:
·· Phase 1 – one thermal energy storage
tank of nominal rated capacity of
100,000 ton-hr charged from Plant 2
with associated thermal energy stor-
age and secondary booster pumps
·· Phase 2 – a second thermal energy
storage tank of nominal rated
capacity of 100,000 ton-hr charged
from Plant 2 with associated thermal
energy storage and secondary
booster pumps
·· Phase 3 – electric-driven centrifugal
chillers with 12,000-ton installed
capacity and associated condenser
water pumps, chiller pumps and
associated secondary booster pumps
Bids for the engineering, procure-
ment, construction and commission-
ing for Phase 1 were called in the
second quarter of 2010, with work
completed in early 2013. Construction
of Phases 2 and 3 is expected to com-
mence in 2017 and 2020, respectively,
depending on the actual load growth
of the Core Island.
At full buildout this three-phase
design will allow for charging the
thermal energy storage tanks with
the 6.1 C (43 F) supply water from
Plant 2, with the ability to peak this
water down to 3.9 C (39 F) using the
Plant 4 chillers while maintaining the
ability to produce chilled water from
Figure 2. Screenshot of Typical Load Profile, GDCP Plant 2, 2009.
Source: Gas District Cooling (Putrajaya) Sdn Bhd.
Buildings Start
Operation
High Peaking Load
Low Night Load

4. 10 District Energy / Fourth Quarter 2015 © 2015 International District Energy Association. ALL RIGHTS RESERVED.
a highly efficient series-counterflow
configuration. This will allow for
significantly larger production stor-
age capacity to be achieved from the
same-sized tanks.
These objectives will be achieved
with a relatively simple piping and
valving configuration and with no
more pumps than would be required
for a traditional primary-secondary
pumping arrangement.
CHALLENGES OF REMOTELY
CHARGING
The design team had to consider
numerous challenges involved in
remotely charging the two chilled-
water storage tanks. From the
hydraulic point of view, the top water
level of each of these atmospheric
tanks had to be at the highest point
of the entire system. Plant 2, which
at 39.2 m (128.6 ft) above sea level is
higher than the 33.6 m (110 ft) above
sea level where the Plant 4 tanks
will be, requires a minimum return
pressure of 3 bar (43.5 psi). Given the
tanks’ height of 32 m (105 ft), the
resultant system’s pressure is more
than adequate to provide sufficient
return pressure to Plant 2.
Another issue of concern was the
system pressure generated during dis-
charge. The combined tank static head
and Plant 4 pump discharge pressure
had to be lower than the existing sys-
tem’s design pressure rating of 16 bar
(232 psi). Numerous simulations using
hydraulic software were conducted
to determine the maximum Plant 4
pump discharge pressure to ensure
that the designed pressure rating was
not exceeded.
The ability of existing pumps at
Plant 2 to move a huge amount of
chilled water through the existing 900-
mm (35.4-inch) pipe during charging
was also evaluated. This was a major
concern especially in Phase 2 when the
two tanks will require charging, as the
most likely path of the chilled water
would be the short distance between
Plant 2 and Plant 4 (see fig. 1). It was
determined that the Plant 2 pump
head was adequate to move charging
and discharging chilled-water flow up
to a certain stage. However, if the load
growth of Precinct 3 and 4 concentrates
mainly at the south end of the Core
Island, Plant 2 pumps will have to be
upgraded depending on the plant send-
out ratio between Plant 2 and Plant 4.
TANK SPECIFICATIONS
The performance specifications
for each of the two chilled-water
storage tank and diffuser systems to
be installed at Plant 4 are shown in
table 1.
Based on the capacity, the speci-
fied tank dimensions were 45 m
(147.6 ft) diameter and 32 m (105.0 ft)
high, with a 700-mm- (27.6-inch-) thick
concrete wall. It is believed that, with
its particular capacity and dimen-
sions, the first of these tanks, com-
pleted in 2013, is the largest water-
retaining structure in Malaysia.
Prestressed concrete was used to
reduce the tank wall thickness. Con-
crete was chosen because it offered
better cost benefit to the owner com-
pared to steel. As Malaysia is not a
steel producer, the cost to import steel
plates would have made this size of
tank uneconomical. A concrete tank
of this size also posed concerns to the
local authorities about its potential for
sabotage as well as leakage. Although
Malaysia is a relatively terrorism-free
country, the authorities insisted that
a risk impact analysis be conducted.
The study concluded that the con-
crete tank is less likely a terrorist
target than the ministry buildings in
Putrajaya. To mitigate any possibility
of leakage, the design team decided to
use two layers of 2-mm (0.078-inch)
and 3-mm (0.118-inch) spray poly-
urea waterproofing membrane, with
50 mm (1.97 inches) of polyurethane
thermal insulation sandwiched in
between. Rigorous inspections and
quality control checks were conducted
during construction to ensure water-
tightness requirements were met.
The storage tank has an internal
stratification diffuser inlet and outlet
header design arranged to distribute
the flow for proper efficient opera-
tion during charging and discharging
modes. The diffuser header design
utilizes a directed flow-splitting
approach to evenly distribute the
water to the nozzles. The nozzles are
distributed radially around the area
centroid of the tank, and the directed
flow-dividing elements of the system
assure that each nozzle is fed with
the same volume of water. The flow
velocity is gradually reduced in the
header system from 1.5 m/s (4.9 ft/s)
55,399 cu m (14.6 million gal)
100,000 ton-hr @ 6.5 C (11.7 F) delta T
4,610 cmh (20,300 gpm)
More than 90% including thermocline,
freeboard and diffuser volume
13.3 C (56 F)
6.1 C (43 F)
6.1 C (43 F)
Maximum 2,000
Less than 2
3.05 m (10 ft) water gauge
2% of rated thermal energy storage
capacity at 3.9 C (39 F)
Spray polyurethane
Spray polyurea
Water Volume
Rated Cooling Storage Capacity
Rated Tank Discharge Flow Rate Capacity Per Hour
Usable Discharge Capacity
Design Inlet Temperature During Discharging Cycle
Design Outlet Temperature During Discharging Cycle
Design Inlet Temperature During Charging Cycle
Reynolds Number
Froude Number
Maximum Pressure Loss Between Inlet and Outlet Flange
Maximum Heat Gain Over 24 Hours
Tank Insulation Material
Tank Waterproof Material
Source: AHAR Consultants.
Table 1. Performance Specifications for GDCP Plant 4 Chilled-Water Storage Tank and
Diffuser System.

5. District Energy / Fourth Quarter 2015 11© 2015 International District Energy Association. ALL RIGHTS RESERVED.
in the feeder pipe to 0.1 m/s (0.33 ft/s)
at the nozzle exit. The large circular
nozzles expel the water parallel to
the water surface or tank base, induc-
ing secondary water movement only
in a parallel layer. Warm water is
withdrawn from the top of the tank,
cooled and reinserted at the bottom
of the tank during the charging cycle.
Cold water is withdrawn from the
bottom of the tank and dispatched to
the buildings, where it is warmed and
returned to the top of the tank during
the discharging cycle.
PHASE 1 PERFORMANCE
After construction of Plant 4
(Phase 1) was completed in early
2013, it was successfully commis-
sioned in March 2013. A typical five-
day charging and discharging cycle in
February 2013 is shown in figure 3.
Figure 3 shows that the load
profile increased to 25,000 tons peak
load early in the morning and aver-
aged around 22,000 ton-hr. (Figure 3
also reflects current load and sendout
capacity.) With the new configura-
tion, this peak load is taken up by
the chilled-water storage discharge
instead of additional chillers run at
Plant 2. Fewer chillers are required
to satisfy daily load, thus enhancing
system availability. There is also a
reduction of 4 MW of electrical power
imported from the electricity compa-
ny. This has significantly reduced the
electrical maximum demand charge
incurred during peak periods, cor-
respondingly lowering the unit util-
ity cost of chilled-water production.
Plant 2 electricity generation effi-
ciency has also improved by having
constant loading of the turbine gen-
erators day and night. The generators
are able to be fully loaded and oper-
ate at optimum efficiency with cooler
nighttime ambient temperatures.
Thermal energy storage tank dis-
charge capacity averaging between
88,000 and 92,000 ton-hr is obtained
daily, with a maximum instantaneous
discharge capacity of 13,000 tons.
With the steam chillers maintaining
a constant output of 14,500 tons day
and night, the gas turbines are able to
be operated 24 hours per day, result-
ing in better utilization and avoidance
of start-stop operations.
The performance of the diffuser
system was also analyzed during the
commissioning period from January
to March 2013. Most of the significant
performance parameters exceeded
the design criteria, as shown in table
2. Most significant is the thermocline
thickness averaging 0.8 m (2.62 ft).
This thin thermocline thickness indi-
cates that the diffusers were working
properly, with the cold and warm
water bodies being properly stratified
in the tank.
A screenshot of thermocline
thickness is shown in figure 4. The
x-axis refers to time, while the y-axis
is the temperature. Various colored
lines represent individual tempera-
ture sensors installed at 0.5-m (1.64-
ft) intervals vertically inside the tank.
By calculating the water volume
and the time spread at each pair of
sensors, the thermocline averages
0.87 m (2.85 ft) thick. In comparison,
thermocline thicknesses of 1-2 m
(3.28-6.56 ft) are not uncommon in
other chilled-water tank installations
worldwide.1
The significance of a thin ther-
mocline is that it yields better storage
efficiency. The diffuser design using
three double-ring octagonal pipes with
drilled 8-mm (0.31-inch) nozzles spray-
Figure 3. Putrajaya Core Island Plants 2 and 4 Load Profile and Sendouts, February 2013.
Source: Gas District Cooling (Putrajaya) Sdn Bhd.
109,012 ton-hr @ 6.5 C (11.7 F) delta T
78,433 ton-hr @ 4.32 C (39.8 F) delta T
72,585 ton-hr @ 4.32 C (39.8 F) delta T
0.6-1.0 m (1.97-3.28 ft)
1,991
0.09
92.54%
2.25 m (7.38 ft) water gauge
0.57% of rated thermal energy storage capacity
Rated Storage Capacity
Charging Storage Capacity
Discharge Storage Capacity
Thermocline Thickness
Reynolds Number
Froude Number
Usable Tank Volume
Maximum Pressure Loss
Maximum Heat Gain Over 24 Hours
Source: AHAR Consultants.
Table 2. Tested Performance of GDCP Plant 4 Chilled-Water Storage Tank and Diffuser
System (Jan. 17, 2013).
1
Bahnfleth, William P., and Amy Musser, “Thermal Performance of a Full-Scale Stratified Chilled-Water Thermal
Storage Tank,” ASHRAE Conference proceeding, Toronto 1998.
Average Plant 2 Sendout Capacity – 14,500 Tons
Chiller Discharge Charging —— Plant Sendout

6. 12 District Energy / Fourth Quarter 2015 © 2015 International District Energy Association. ALL RIGHTS RESERVED.
ing at a 120-degree angle in the vertical
plane proved that the actual perfor-
mance exceeded specifications. A total
of 91,500 nozzles ensure that the water
is evenly distributed and diffused.
At this juncture, the objective for
better chilled-water supply tempera-
ture control has not yet been accom-
plished, as Plant 4 is still dependent
on Plant 2 for its chilled water. It is
envisaged that when the electric
chillers are installed at Plant 4 in the
ultimate phase – where the chillers
can be operated either in parallel or
in series-counterflow configurations
with the storage tank – this design
intent can also be achieved.
MEETING EXPECTATIONS
Plant 4 has been in operation to
supply chilled water to Precincts 3
and 4 in Putrajaya Core Island since
January 2013. Initial results have
shown that the operation of this
chilled-water storage system has met
the expectations of the client and
design team. Currently, Plants 2 and
4 are operating in tandem during the
daytime to supply chilled water.
The installation of chilled-water
storage in a district cooling system is
an excellent tool in demand-side
management. This technology
enables a plant owner to reduce
energy cost by decreasing electric-
ity maximum demand during peak
periods. Thermal energy storage also
increases the load supply capability
during the high peak period and
enhances district cooling system reli-
ability and availability.
By incorporating thermal energy
storage, GDCP has improved system
redundancy, as fewer chillers are
required during the peak period. The
company is also better able to utilize
the assets at Plant 2 by running the
gas turbines 24/7. Daily start-stop
operation of the gas turbines has
been avoided, improving equipment
life expectancy. Furthermore, the use
of chilled-water storage has reduced
net capital expenses by 40 percent
compared to installation of an equiv-
alent capacity of conventional chiller
plant equipment. The chilled-water
production unit cost remains similar
to the pre-Plant 4 period, despite the
operation of both plants.
In addition to these operational
and financial advantages, GDCP is also
seeing reduced greenhouse gas emis-
sions. The use of thermal energy stor-
age at Plant 4 with chilled-water gener-
ation from Plant 2 offers a significantly
decreased carbon footprint – lower by
445 metric tons of carbon dioxide per
week, or 20.7 percent – compared to
that of a grid-connected conventional
chiller Plant 4 and the existing Plant 2.
While providing these numerous
benefits, GDCP Plant 4 has also, sig-
nificantly, made history as the first
remotely charged satellite chilled-
water storage system in Malaysia and
has the biggest reinforced concrete
chilled-water tank in the country, as
well as in Asia.
Authors’ Note: We acknowledge the
assistance provided to AHAR Consul-
tants during the evaluation, design and
implementation of the Plant 4 thermal
energy storage project, in particular by our
engineering team members Mark Spurr
and Bryan Kleist of FVB Energy Inc., Min-
neapolis, Minn., and John S. Andrepont of
The Cool Solutions Co., Lisle, Ill. We also
thank John Andrepont (with whom one of
the authors collaborated on the first large
chilled-water thermal energy storage proj-
ect in Malaysia in the mid-1990s) for his
contributions to the content and writing of
this article.
Arul Hisham Abdul
Rahim, principal with
AHAR Consultants, has a
wide range of experience in
thermal storage and district
cooling with more than 20
years of practice. A regis-
tered engineer with the Board of Engineers
Malaysia, he is a member of ASHRAE and
a fellow with the Institution of Engineers
Malaysia. He holds a degree in mechanical
engineering from The University of Texas
at El Paso. Hisham can be contacted at
arulhisham@aharconsultants.com.
Rosli Mohamed, partner
with AHAR Consultants,
graduated from the
University of North
Carolina at Charlotte in
mechanical engineering.
Prior to joining the firm, he
worked in various capacities with Tenaga
Nasional Berhad, Malaysia’s national elec-
tricity company. He is a fellow with the
Institution of Engineers Malaysia and a
registered engineer with the Board of
Engineers Malaysia. He can be reached at
roslimohamed@aharconsultants.com.
Figure 4. Screenshot of GDCP Plant 4 Thermal Energy Storage Tank Temperature Sensor
Readings.
Source: AHAR Consultants.