This document summarizes a study evaluating heat loss in the piping system of the Wayang Windu Geothermal Field in Indonesia. The study found that insulation on the steam pipes is damaged, allowing heat to escape and reducing electricity production. Calculations were done to determine the heat loss and potential generation losses at different air velocities and insulation conditions. The financial loss from reduced electricity production due to heat loss through damaged insulation was estimated to be around $99,781 per year based on the selling price of electricity.

1. Proceedings The 4th
Indonesia International Geothermal Convention & Exhibition 2016
10 - 12 August 2016, Cendrawasih Hall - Jakarta Convention Center, Indonesia
1
EVALUATION OF ENERGY LOSS
IN GEOTHERMAL PIPING SYSTEM
(Case Study at Wayang Windu Geothermal Field)
Willy Ardiansyah, Mahendra Kuntoaji, Hariyanto
Starenergy Geothermal Wayang Windu
mahendra.kuntoaji@gmail.com
Keywords: Heat loss geothermal power plant, steam pipe
insulation, Wayang Windu.
ABSTRACT
Heat lost along geothermal pipe line is significant potential
generation opportunity losses. Production well distance with
power plant, broken and or stolen insulation caused
significant potential heat due to difference temperature
vapor and ambient temperature. The insulation protect heat
loss from the steam, however there was damage and or
stolen along pipe line that caused reduce production
electricity.
The case base on operational of Wayang Windu Geothermal
Power Plant in west Java Indonesia. Steam pipe insulation
system of Wayang Windu Geothermal Power Plant consists
of calcium silicate layers with thickness of 50 mm where the
outer part is covered by aluminum sheet with thickness of 2
mm. The heat loss estimation calculate base on conduction
and convection to the piping that interference by ambient
temperature. The energy balance base on steam flow
quantity inside piping that interference by ambient
temperature thus some of steam condense. Compere with
generation electricity output. Financial assement to
determine opportunity losses calculated based on energy
price help to justified whether the insulation to be repaired
on damage and or stolen area.
Thermal resistance of pipe insulation system of Wayang
Windu Geothermal Power Plants is dominated by
conduction resistance of insulation and convection resistance
of air around the pipes. Hence, heat loss through the steam
pipe is strongly influenced by the condition of the insulation
and the air velocity around the pipe. The financial loss due
to loss of electricity production at average air velocity when
the selling price is 0.06 USD/kWh is 99,781 USD/year.
These paper analyze of potential process loss caused by
damaged of insulation in the steam piping geothermal
operation.
BACKGROUND
At this time, there is damage to the insulating layer of steam
pipelines between wells and separators. This damage occurs
because of the loss of the pipe blanket made of aluminum
sheet in a few places. The question is whether the damage
cause significant impact on electricity production of Wayang
Windu Geothermal Power Plant. Some of energy contained
in the steam will be lost on the way from the well to the
turbine due to heat transfer from the pipe to the environment
outside of the pipe.
This paper will examine the above problem. The results
of the study will provide information about how much
energy has been lost that can be used as a basis to improve
the pipe insulation system.
STEAM PIPING SYSTEMS OF WAYANG WINDU
GEOTHERMAL POWER PLANT
Wayang Windu Geothermal Power Plants generate
electricity through a steam turbine driven by the steam
coming from several wells. These wells located around the
power plants with different distances. Vapors from these
wells are almost dry with the quality above 97%. Fig 1
shows the steam piping system of Wayang Windu
Geothermal Power Plants.
Fig 1 Steam piping system of Wayang Windu Geothermal
Power Plant
From these wells, the steam flows through the piping
system to the separator where the steam and condensate is
separated. Steam coming out of the separator is at saturated
vapor, while the condensate discharge from the separator is
at saturated liquid. Saturated steam then flows to the
demister (scrubbers) before is supplied to the turbine.
The distance of the wells to the Wayang Windu Geothermal
Power Plants vary but all are quite far from the power plants
so that there is a potential for heat loss from the steam due to
the difference in the vapor and ambient air temperature. To
reduce the heat loss, the outer surface of the pipe fitted with
insulation and the outer portion of the insulation is covered
with a sheet of aluminum. Fig 2 shows the structure of the
pipe with insulation and cover. It can be seen from the cross-
sectional images that the steam pipe material is made steel
while the calcium silicate insulation is made of aluminum
while the lid is made of aluminum.
Fig 2 Structure of straight pipe insulation
on steam piping system
Wayang Windu Geothermal Power Plant steam piping
located around the tea plantation area managed by forestry
so it is quite difficult for the Wayang Windu management in
monitoring the steam piping. At this time, there has been
damage to the pipe insulation in various places due to the

2. Proceedings The 4th
Indonesia International Geothermal Convention & Exhibition 2016
10 - 12 August 2016, Cendrawasih Hall - Jakarta Convention Center, Indonesia
2
loss of the insulating cover made of aluminum. If this cover
is broken then the insulation made of calcium silicate will be
separated from the outer surface of the pipe. As a result, the
outer surface of the pipe will be exposed to the surrounding.
Damage to the pipe insulation will cause a rise in heat
loss of the steam. Because the steam coming from the well is
at two-phase fluid (saturated vapor and saturated liquid), the
increase in heat loss will increase the rate of condensation of
the steam. The amount of liquid that is formed as steam
flowing from the well to the separator will increase. Hence,
the fraction of steam from the top of the separator will be
reduced proportional to the fraction of liquid that comes out
from the bottom of the separator. Because the vapor fraction
is reduced due to the rate of condensation, the steam flowing
to the turbine will also be reduced. As a result, production of
electricity of the power plant will be reduced as well.
Since the end product of the geothermal power plant is
electrical energy, steam pipe insulation damage that reduces
production of electricity should be repaired. However,
because this repair needs costs, it is necessary to do the
calculations to determine its financials feasibility. This
report provides the information necessary to perform
financial calculations later so that decision to repair the
insulation damaged can be made properly.
PRINCIPLES OF HEAT LOSS ESTIMATION
The rate of heat loss from the steam flowing inside the
steam piping system can be estimated from the calculation
of heat rate by conduction and convection. The heat loss due
to radiation can be neglected since the surface temperature
of the outside pipe is quite low (below 200oC).
Conduction heat transfer rate can be estimated from the
following equation:
Where:
• Qconduction : conduction heat transfer rate
• k : thermal conductivity of material
• As : heat transfer surface area
• T1 and T2 : high and low temperature
• ∆x : thickness of material
For geometry with curved surfaces and outer and inner
diameter d1 and d2 respectively, conduction heat transfer rate
equation is as follows:
With L is the length of the segment that plays a role in heat
transfer process. While the convection heat transfer rate can
be estimated from the following equation:
Where:
• qconvection : convection heat transfer rate
• h : convection heat transfer coefficient
• As : heat transfer surface area
• Ts : surface temperature
• Tair : surrounding air temperature
To facilitate the calculation of the rate of heat transfer
through conduction and convection processes
simultaneously, the rate of heat transfer equation through a
pipe can be expressed in terms of the analogy of electricity
(Ohm's Law) as follows:
Where thermal resistance of conduction and convection are:
For the calculation of heat transfer rate from the steam to
the surrounding in the steam piping system of Wayang
Windu Geothermal Power Plant, Fig 3 can be used. The
figure describes the process of heat transfer from the vapor
to the air through an uninsulated pipes with its thermal
circuit. R1 and R4 show the thermal resistance of conduction
and convection respectively.
Fig 3 Thermal circuit for uninsulated pipe
Then the rate of heat transfer from the vapor to the air can be
calculated as follows:
where Rtotal is the sum of conduction resistance R4 and
convection resistance R1, which is:
For an insulated pipe, the heat transfer rate calculation can
be performed by observing Fig 4.
Fig 4 Thermal circuit for an insulated pipe.
The rate of heat transfer from the vapor to the air can be
calculated as follows:
where Rtotal is the sum of conduction resistance R2, R3, and
R4, and convection resistance R1, which is:
where:
• d1 : inner diameter of pipe
• d2 : outer diameter of pipe

3. 3
• d3 : outer diameter of insulation
• d4 : outer diameter of lid
• k : thermal conductivity of each materials
Convection coefficient in convection thermal resistance
equation must be estimated before the resistance value can
be calculated. Estimated value of the convection heat
transfer coefficient depends on the geometry, fluid
properties, and the condition of the air around the pipe.
When air flows at a certain velocity then it is called forced
convection while if air is not flowing then it is called free
convection.
For forced convection, correlations to predict the
convection heat transfer coefficient is as follows:
with:
V is the velocity of the air around the pipe with diameter D
and k and Ʋ are conductivity and kinematic viscosity of the
air, respectively. Pr is the Prandtl number of air. From the
above relationship the value of the convection heat transfer
coefficient h can be estimated.
ENERGY BALANCE OF STEAM PIPING SYSTEMS
Loss of heat energy from the steam to the surrounding air in
the piping system of Wayang Windu Geothermal Power
Plants need to be converted into loss of electricity
production. As can be seen in Fig 1, there are many wells
that produce steam which eventually collected and flow into
the separator in the power plants area. Energy balance
calculation can be simplified by defining the system
boundary as shown in Fig 5.
1 32
qloss,1 qloss,2
Fig 5 System boundary to simplify the calculation
of heat balance
Steam from various wells after passing the measuring
devices (flow meter) is described as out of the component
(1) and then enter component (2) which describes the steam
piping system of Wayang Windu Geothermal Power Plants.
Then, the steam exits the piping system and enters
components (3) which describes separator. The focus of
attention for the analysis of electricity production loss due to
heat loss in steam piping system is the component (2). qloss,1
is the rate of heat loss in good insulated pipe conditions
along L and qloss,2 is the rate of heat loss in damaged pipe
insulation condition along L.
If the pipe insulation is damaged then the rate of heat
loss will increase by qloss,2 and when the steam exits the
component (2), part of the steam will condenses at a rate
comparable to the rate of heat loss. Thus, the rate of steam
entering the separator will decrease proportional to the rate
of addition of the condensation.
The energy balance for the steam piping system of
Wayang Windu Geothermal Power Plants for damaged
insulation condition can be expressed by the following
relationship:
While the energy balance for the piping system with good
insulation conditions are as follows:
Addition of condensation rate due to the heat loss qloss,2
can be determined from the following relationship:
With hfg is heat of condensation at operational pressure.
The amount of electricity production loss due to damage to
the pipe insulation can be determined from the following
equation:
Thus, electricity production loss can be determined directly
if the addition of condensation rate and turbine entry and
exit enthalpy are known.
RESULT AND DISCUSSIONS
The increase in the heat loss due to damaged insulation
can be determined from the calculation of heat loss at
damaged insulation condition minus the heat loss at good
insulation condition. For Unit 2, from Table 4 and Table 5 it
can be shown that the total heat loss in good insulation
condition is 61,9 kW and in damaged insulation condition is
304,2 kW. Thus, the increase in heat loss 304,2 kW – 61,9
kW = 242,3 kW. For the calculation of the other conditions,
the procedure is the same and only changed the air velocity.
Increase in heat loss due to damaged insulation at
various air velocities are presented in Table 6 for Unit 1 and
Table 7 for Unit 2.
From these calculations it can be seen that the heat loss
is strongly influenced by the condition of the pipe insulation
and air velocity around the pipe. For the same total length of
damaged insulation, the higher the air velocity, the higher
heat loss from the steam to the surrounding air will be.
Table 1 Calculation of heat loss at average air velocity at
good insulation (Unit 2)
ØDo ØDi h R1 R2 R3 R4 Rtotal qloss
AREA DRAWING LENGTH(m) (mm) (mm) (W/m2K) (K/W) (K/W) (K/W) (K/W) (K/W) (kW)
WW2-ME-70-104 9 914.40 882.64 66654 183.8 4.75 3.63197E-05 0.031643317 3.39484E-07 0.00771 0.03939 4.34
9 914.40 882.64 66654 183.8 4.75 3.63197E-05 0.031643317 3.39484E-07 0.00771 0.03939 4.34
4 914.40 882.64 66654 183.8 4.75 8.17193E-05 0.071197464 7.6384E-07 0.017348 0.088628 1.93
13.2 914.40 882.64 66654 183.8 4.75 2.47634E-05 0.021574989 2.31467E-07 0.005257 0.026857 6.37
18.6 914.40 882.64 66654 183.8 4.75 1.7574E-05 0.015311283 1.64267E-07 0.003731 0.01906 8.97
20.6 914.40 882.64 66654 183.8 4.75 1.58678E-05 0.01382475 1.48318E-07 0.003369 0.017209 9.94
14.901 914.40 882.64 66654 183.8 4.75 2.19366E-05 0.01911213 2.05044E-07 0.004657 0.023791 7.19
WW2-ME-70-105 20.1 914.40 882.64 66654 183.8 4.75 1.62625E-05 0.01416865 1.52008E-07 0.003452 0.017637 9.70
7.92 914.40 882.64 66654 183.8 4.75 4.12724E-05 0.035958315 3.85778E-07 0.008762 0.044761 3.82
WW2-ME-70-106 11 914.40 882.64 66654 183.8 4.75 2.97161E-05 0.025889987 2.7776E-07 0.006308 0.032228 5.31
128.321 Totalheatloss U2 61.9
ReD NuD
TotalLength
LISTOFLOSTCLADDING
MBBtoJ.20
Table 2 Calculation of heat loss at average air velocity and
damaged insulation (Unit 2)
ØDo ØDi h R1 R4 Rtotal qloss
AREA DRAWING Service LENGTH(m) (mm) (mm) (W/m2K) (K/W) (K/W) (K/W) (kW)
WW2-ME-70-104 TwoPhase Mains 9 914.40 882.64 59847 168.5 4.847 3.63197E-05 0.007979 0.008016 21.33
9 914.40 882.64 59847 168.5 4.847 3.63197E-05 0.007979 0.008016 21.33
4 914.40 882.64 59847 168.5 4.847 8.17193E-05 0.017953 0.018035 9.48
13.2 914.40 882.64 59847 168.5 4.847 2.47634E-05 0.00544 0.005465 31.29
18.6 914.40 882.64 59847 168.5 4.847 1.7574E-05 0.003861 0.003878 44.09
20.6 914.40 882.64 59847 168.5 4.847 1.58678E-05 0.003486 0.003502 48.83
14.901 914.40 882.64 59847 168.5 4.847 2.19366E-05 0.004819 0.004841 35.32
WW2-ME-70-105 TwoPhase Mains 20.1 914.40 882.64 59847 168.5 4.847 1.62625E-05 0.003573 0.003589 47.65
7.92 914.40 882.64 59847 168.5 4.847 4.12724E-05 0.009067 0.009109 18.77
WW2-ME-70-106 TwoPhase Mains 11 914.40 882.64 59847 168.5 4.847 2.97161E-05 0.006528 0.006558 26.07
128.3 Totalheatloss U2 304.2
ReD NuD
LISTOFLOSTCLADDING
MBBtoJ.20
Total Length

4. Proceedings The 4th
Indonesia International Geothermal Convention & Exhibition 2016
10 - 12 August 2016, Cendrawasih Hall - Jakarta Convention Center, Indonesia
4
Table 3 Increase in heat loss at various air velocity (Unit 1)
Air Velocity
(m/s)
Heat Loss Good
Insulation (kW)
Heat Loss damaged
Insulation (kW)
Increase in
Heat Loss (kW)
Remark
0 68,8 126,3 57,5 Minimum
1,04 119,5 586,6 467,1 Average
2,97 134,5 1357,4 1222,9 Maximum
Table 4 Increase in heat loss at various air velocity (Unit 2)
Air Velocity
(m/s)
Heat Loss Good
Insulation (kW)
Heat Loss damaged
Insulation (kW)
Increase in
Heat Loss (kW)
Remark
0 35,7 65,6 29,9 Minimum
1,04 61,9 304,2 242,3 Average
2,97 69,7 703,7 634,0 Maximum
Loss of power production can be determined from the
increase in heat loss. As explained in the previous section,
the increase in heat loss will increase the rate of
condensation of steam in the pipe from the wells to the
separator. This section presents an example of the
calculation of loss of electricity production at average air
velocity.
From the previous calculations it is known that for Unit
1, the increase in heat loss due to damage of the pipe
insulation on the average air velocity is equal to 467,1 kW.
On average vapor pressure of 19.92 bara (or 19.12 barg,
assumed atmospheric pressure of 0.8 bara), condensation
heat of water is equal to 1891 kJ/kg. Thus, the addition rate
of condensation can be determined as:
Loss of electricity production for Unit 1 and Unit 2 due
to steam rate reduction is calculated with the following
assumptions:
• Turbine adibatic efficiency: 80,2% (Unit 1) and
0,792 (Unit 2)
• Turbine mechanical efiiciency: 98,9%
• Generator efficiency: 98,7%
• Steam Inlet pressure to the turbine: 10,4 bara
(Unit 1) and 10,425 (Unit 2)
• Steam Inlet quality to the turbine: saturated vapor
• Steam outlet pressure from the turbine: 0,12 bara
(Unit 1) and 0,11 (Unit 2)
The calculation are given in separated spreadsheet
attached to this report where additional condensation rate
and loss of electricity production can be found. For both
Unit 1 and Unit 2, additional condensation rate and loss of
electricity production is summarized in Table 11.
Table 5 Summary of additional condensation rate and loss of
electricity production
Unit 1 Unit 2 Unit 1 Unit 2 Total
0 0.029 0.015 15.3 8.1 23.4 Minimum
1,04 0.235 0.123 124.6 65.2 189.8 Average
2,97 0.616 0.322 326.5 170.7 497.2 Maximum
Additional Condensation
Rate (kg/s)
Air Velocity
(m/s)
Remark
Loss of Electricity Production (kW)
As can be seen in Table 8, the maximum loss of
electricity production for Unit 1 and Unit 2 are 326,5 kW
and 170,7 kW, respectively. Although at a maximum air
velocity, the increase in heat loss from the steam to the air
reaches 1222,9 kW for Unit 1 and 634,0 kW for Unit 2, the
maximum loss of power production is only around 28% of
the maximum increase in heat loss. This is because the latent
heat of condensation is much greater than the decrease in the
enthalpy of the steam expansion process within the turbine.
It should be noted here that the loss of electricity production
is only for the damaged section of pipe insulation, not for
the entire pipelines from the wells to the turbines of Wayang
Windu Geothermal Power Plants.
To give a picture of financial loss due to loss of
electricity production, it is assumed that electricity selling
price is 6 cUSD/kWh. Taking average air velocity as basis
of calculation, the financial loss per year becomes: 0.06
USD/kWh x 189.8 kW x 24 h x 365 h/year = 99,781
USD/year.
CONCLUSIONS
• Steam pipe insulation system of Wayang Windu
Geothermal Power Plant consists of calcium
silicate layers with thickness of 50 mm where the
outer part is covered by aluminum sheet with
thickness of 2 mm.
• Thermal resistance of pipe insulation system of
Wayang Windu Geothermal Power Plants is
dominated by conduction resistance of insulation
and convection resistance of air around the pipes.
Hence, heat loss through the steam pipe is
strongly influenced by the condition of the
insulation and the air velocity around the pipe.
• The financial loss due to loss of electricity
production at average air velocity when the
selling price is 0.06 USD/kWh is 99,781
USD/year.
REFERENCES
[1] Introduction to Heat Transfer, Incropera and
DeWitt Sixth Edition, John Wiley and Sons Inc.,
2011.
[2] Fundamental of Thermodynamics Engineering,
Moran and Saphiro 5th
Edition, John Wiley and
Sons, 2006.
GLOSSARY
• Vapor is the gaseous phase of water.
Water vapor can be produced from the
evaporation or boiling of liquid water or from
the sublimation of ice.
• Conduction is transferring some of heat to these
neighboring particles trough a conductive
material.
• Convection, is the transfer of heat from one place
to another by the movement of fluids, a process
that is essentially the transfer of heat via mass
transfer.