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Building and Environment 42 (2007) 1644–1653

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Evaluation of the impact of internal partitions on energy conservationfor residential buildings in Serbia

Milorad Bojica,�, Milan Despotovica, Jovan Malesevica, Dusan Sokovicb

aFaculty of Mechanical Engineering at Kragujevac, University of Kragujevac, Sestre Janjic 6, 34000 Kragujevac, Serbia and MontenegrobSokovic Studio, Karadjordjeva 19, 34000 Kragujevac, Serbia and Montenegro

Received 26 July 2005; received in revised form 10 January 2006; accepted 17 February 2006

Abstract

In Serbia, around 50% of energy is used in built environment and most of it for 6-month heating in residential buildings. Because of

actual international efforts to protect environment, energy conservation in heating in residential buildings is an issue of permanent

research interest. In this paper, we tried to determine how type of partitions inside a residential building influences energy consumption

and demand for houses in cold climate and consequently energy conservation. For a typical house in Serbia, by using software HTB2, it

was evaluated how its heating depends on six applied types of partitions. It was found that (1) the house with glass-wool partitions would

have the minimum yearly heat consumption, (2) the house with masonry partitions would require heaters of minimum size, (3) the house

with siporex partitions would require the lowest investment in partitions and heaters, and (4) the house with glass-wool partitions would

yield the highest net savings during the life cycle of the house.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Building envelope; Heaters; Residential buildings

1. Introduction

In Serbia, energy used in built environment representsaround 50% of total used energy. During last years, thispercentage rises continuously. In residential buildings, thelargest part of energy is used for heating as the heatingseason lasts 6 months. Because of actual internationalefforts to protect environment, heating of buildings is anissue of permanent interest to the government of Republicof Serbia and its ministries. Serbian Ministry for Miningand Energy founded the Serbian Agency for EnergyEfficiency in 2002 where one of its activities is to increaseenergy efficiency in buildings [1]. Furthermore, SerbianMinistry of Science, Technology and Development givesprominent funds to universities in Serbia to work onNational Research Programs in Energy Efficiency. One ofthese programs is Energy Efficiency in Built Environmentthat would be active in this and subsequent years [2].

e front matter r 2006 Elsevier Ltd. All rights reserved.

ildenv.2006.02.006

ing author. Tel./fax: +381 34 330 196.

ess: bojic@kg.ac.yu (M. Bojic).

The best way to have energy-efficient building is to startwith its energy-efficient design. To check energy andenvironmental performance of some building in its designstage, we may use building energy simulation programssuch as HTB2, DOE2, Energy Plus, etc. Among multitudeof issues of energy-conscious design, the most interestingissue for architects is an issue of building envelope andbuilding partitions.While an influence of building envelope on energy

consumption was studied often [3,4], the influence ofpartitions on energy consumption and demand was studiedrarely and only for hot and humid climate [5–7]. Theresearch presented in this paper is the first such attempt forcold climate.For six typical small buildings (houses) in Serbia (with

two flats), research was performed on their heating. Eachof these six houses differs only in composition of itspartitions obtained from architectural design studio inKragujevac, Serbia as these are applied in real buildings [8].For each house, we will evaluate the following: (1) the heatcapacity and overall U value of its partitions, (2) its yearlyheat consumption, (3) size of heaters, and (4) investment

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Nomenclature

A size of partitions in m2

CQ costs for heating during life of house, presentvalue h

CQ6CN CQ for the house with concrete partitions,present value h

D power of radiators, Wd depreciation ratee escalation rate of district heating pricesI hourly time intervalID cost for investment in radiators, present value hIP cost for investment in partitions, present value hIT cost for investment in both partitions and

radiators, present value h

IT6CN IT for the house with concrete partitions,present value h

J room index

LCC life-cycle cost, present value h

LCC6CN life-cycle cost for the house with concretepartitions , present value h

N total number of heated roomsNB number of heated rooms in the buildingN1 number of heated rooms in the first-floor flatN2 number of heated rooms in this flatNS net savings, present value h

n entire house life, yearsQ yearly energy consumption for some building, WhQI,J heat consumption (an output of HTB2) of room

J during hourly time I, WhQmax maximum yearly energy consumption among

the investigated buildings, WhQmax,J max (QI,J) where I ¼ 1,y,8760.tp cost of m2 of partition, present value h/m2

td cost of heating power, present value h/Wtq cost of heat, present value h/Wh

M. Bojic et al. / Building and Environment 42 (2007) 1644–1653 1645

costs in partitions and heaters. Moreover, for each house,we would additionally obtain: (1) drop in investment costsin partitions and heaters relative to that for the house withthe most expensive investment costs in partition andheaters, (2) drop in costs for heating relative to that forthe house with the highest heating costs, and (3) net savingsrelative to that for the house with the highest life-cyclecosts.

2. The simulation software HTB2

The simulation software HTB2 [9] is dynamic buildingenergy software that can account for complex time-varyingclimatic and occupation conditions in the prediction ofheating and cooling loads, and indoor environmentalconditions in a building. The building fabric model usesthe finite-difference method to solve the one-dimensionaldynamic heat conduction equation for modeling heattransfer through the fabric elements, which could becomposed of multiple layers of different materials. Themodel can predict the thermal performance of a buildingwhen it is subject to the influence of outdoor temperature,solar gain, shading, ventilation, and infiltration. It alsoallows the user to define complex cooling and heatingschedules, occupancy, lighting, and internal load intensitypatterns, and to vary control settings during run-time, tomimic realistic occupation conditions.

In order to allow a year-round simulation to beaccomplished efficiently, there are necessary limitationsimposed by the assumptions implicit in the algorithm.Similar to other simulation models, HTB2 assumes that theair temperature within each simulated zone is uniform.Radiation and convection are taken into account indepen-dently. The solar gains are distributed over the wallsaccording to decision of a user. The software supports

several types of control thermostats: on/off, ideal, andproportional. The software does not simulate heatingsystems in operation, but gives the energy that should beprovided to the building by a heating system. HTB2 hasbeen shown to be able to yield predictions that mach wellwith measurements for buildings in cold climate [10].

3. Simulation arrangement

Inputs for HTB2 were prepared for 6 houses designatedas 1IN, 2SC, 3SP, 4GB, 5BK, and 6CN. These houses onlydiffered in constructions of partitions. All their othercharacteristics were the same, such as layout, use patterns,and external envelope composition.

3.1. Layout

A contemporary residential house (low-rise building) inSerbia is shown in Fig. 1. The house has two stories andcomprises two identical apartments, where one is on its firstand another on its second floor. The plans of theseapartments are shown in Fig. 2. Each flat consists of twobedrooms B1 and B2, one living room L, one kitchen K,one bathroom T, and one anteroom A. One corridor Ccontains stairs serving both apartments. The sizes ofinvestigated flats and their rooms are given in Table 1. Itwas assumed that each flat, which has a total floor areaaround 54m2, would accommodate a family of four: twoworking adults and two children.

3.2. Use patterns

Each flat has the same patterns of occupancy, lighting,and small power, and are shown in Tables 2–4.

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SIDE VIEWFRONT VIEW

SIDE VIEWREAR VIEW

Fig. 1. Typical contemporary house in Serbia.

L

S

N

W E

L

The first floor apartment

The second floor apartment

L-Living room

B1-Bedroom 1

B2-Bedroom 2

K-Kitchen

T-Toilet

A-Anteroom

C-Corridor

K T B1 K T B1

A A

C B2 C B2

Fig. 2. Plans of the first- and second-floor apartment of the investigated

house.

Table 1

Size (in m2) of investigated flat at the first floor and their roomsa,b

Room Size (m2)

Living room 21.9

Bedroom 1 8.7

Bedroom 2 10.2

Kitchen 5

Bathroom 3.7

Anteroom 4.2

S 53.7

aSize of the flat and its rooms at the second floor is assumed to be the

same.bSize of the corridor with stairs at the first floor was 6.8m2 and at the

second floor 9.3m2.

M. Bojic et al. / Building and Environment 42 (2007) 1644–16531646

3.3. Heating and ventilation

The assumption was that all rooms used heaters thatwere ideally controlled by thermostats. The room tempera-tures were set as shown in Table 5. The heaters dailyoperated from 6:00 to 22:00 h, i.e., their operation did notdepend on the room occupancy. This heating pattern wascharacteristic of radiators served by district heating.Heating was run only during 6-month heating season:from October 15th until April 15th.

The assumption was that during heating season, allrooms were naturally ventilated with periodically openwindows. The ventilation and infiltration rates were as inTable 6.

3.4. Envelope

Each house had the same composition of its envelope,doors, windows, floor, ceilings, and roof. The compositionsof non-modified constructions are given in Table 7. Thecharacteristics of the various layers of materials used indifferent constructions of the studied houses are givenTable 8.

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Table 2

Pattern of occupancy for the flat at the first floora,b

Time Number of occupants

Living room Kitchen Toilet Bedroom 1 Bedroom 2 Anteroom

00:00–07:00 0 0 0 2 2 0

07:00–08:30 2 1 1 0 0 0

08:30–09:00 0 0 1 0 0 0

09:00–16:00 0 0 0 0 0 0

16:00–22:00 4 0 0 0 0 0

22:00–24:00 0 0 0 2 2 0

aOccupancy pattern for the flat at the second floor is assumed to be the same.bCorridor for each floor is assumed to be unoccupied all the time.

Table 3

Pattern of use of lighting load for the flat at the first floora,b

Time Lighting load (W)

Living room Kitchen Toilet Bedroom 1 Bedroom 2 Anteroom

00:00–18:00 0 0 0 0 0 0

18:00–19:00 200 150 100 0 0 100

19:00–20:00 200 150 0 0 0 100

20:00–22:00 200 0 0 0 0 100

22:00–23:00 200 0 0 120 120 100

23:00–24:00 0 0 0 120 120 0

aLighting-load pattern for the flat at the second floor is assumed to be the same.bCorridor for each floor has a lighting load of 100W from 18:00 to 23:00 h; otherwise it is without lightning load.

Table 4

Pattern of use of small-power load for the flat at the first floora,b

Time Small-power load (W)

Living room Kitchen Toilet Bedroom 1 Bedroom 2 Anteroom

00:00–08:00 0 0 0 0 0 0

08:00–12:00 0 1700 0 0 0 0

12:00–18:00 0 0 0 0 0 0

18:00–19:00 150 0 0 0 0 0

19:00–22:00 0 0 0 0 0 0

22:00–23:00 150 0 0 100 0 0

23:00–24:00 0 0 0 100 0 0

aSmall-power-load pattern for the flat at the second floor is assumed to be the same.bCorridor for each floor does not have any small power load.

Table 5

Temperatures maintained in different rooms

Room Temperature (1C)

Living room 20

Bedroom 1 20

Bedroom 2 20

Kitchen 20

Bathroom 24

Anteroom 15

Corridor 10

M. Bojic et al. / Building and Environment 42 (2007) 1644–1653 1647

3.5. Partitions

Each house had different composition of its partitions.House 1IN had glass-wool partitions (using outer gypsum-plaster layers), house 2SC siporex partitions using outercement layers, house 3SP siporex partitions using outerplaster layers, house 4GB breeze-block partitions (usingouter plaster layers), house 5BK brick partitions (using outerplaster layers) and house 6CN concrete partitions. For eachhouse, the compositions of the partitions are given in Fig. 3together with their overall U values and heat capacity (C).

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Table 6

Ventilation in ach/ha

Infiltration Ventilation rate 1 Ventilation rate 2

Living room 1.25 1.0 5.0

Bedroom 1 0.75 0.75 5.0

Bedroom 2 0.75 0.75 5.0

Kitchen 1.00 1.5 5.0

Bathroom 0.75 0.75 5.0

Attics 2.0 2.0 2.0

aVentilation rate 1 was enabled during heating from 8:30 to 18:00 h, otherwise only infiltration ventilation rate was enabled. The ventilation rate 2 was

enabled when temperature in some room was above 25 1C.

Table 7

Compositions of non-modified constructions

Layers Constructions

Envelopea Doors Windows Floorc Ceiling 1c Ceiling 2c

1 Polystyrene, 60mm Wood, 6mm Glass, 3mm Wood block, 24mm Thermalite, 100mm Wood block, 24mm

2 ACBb, 250mm Air cavity, 38mm Air cavity, 30mm Concrete (light), 30mm Concrete (heavy), 40mm Thermalite, 20mm

3 Plaster light, 15mm Wood, 6mm Glass, 3mm PVC, 1mm ACB, 160mm Concrete (heavy), 40mm

4 Thermalite, 60mm ACB, 160mm

5 Bitumen felt, 2mm Plaster light, 15mm Plaster light, 15mm

6 Concrete (heavy), 40mm

7 Granolithic screed of 50mm

aThe first layer faces outdoors and the last indoors.bACB: Aerated concrete block.cFor floor and ceilings, layers are listed from top to bottom.

Table 8

Values of parameters of the layers used in simulations

Layer Specific heat capacity (J/kg-K) Density (kg/m3) Thermal conductivity (W/K-m)

Brick (inner leaf) 1800 840 0.62

Breeze block 1500 650 0.44

Bitumen felt 1700 1000 0.5

Concrete (heavy) 2100 653 1.400

Concrete (light) 1200 653 0.38

Aerated concrete block 750 1000 0.24

Granolithic screed 2085 837 0.87

Cement screed 2100 650 1.400

Clay tiles 1900 837 0.85

Plaster dense 1300 1000 0.5

Plaster light 600 1000 0.16

Gypsum plastering 1200 837 0.42

Wood block 800 2093 0.16

Glasswool 250 840 0.04

Thermalite 753 837 0.03

Siporex 550 1004 0.12

Pvc 1379 1004 0.16

Polystyrene 25 1380 0.03

Window glass 2500 750 1.050

M. Bojic et al. / Building and Environment 42 (2007) 1644–16531648

4. Results and analysis

On the basis of characteristics of the houses definedabove, the yearly heating load and power of radiators havebeen predicted by using HTB2 based on hourly weatherconditions in Belgrade, Serbia [11]. Furthermore, the

investment cost for partitions, investment cost for radia-tors, total investment cost in partitions and radiators, thedrop in the total investment cost in partitions and radiatorsfrom the maximum recorded value, costs for heatingduring the building life cycle, drop in costs for heatingduring the building life cycle from the maximum recorded

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House 1IN

Gypsum plastering(10mm)

Glass wool (80mm)

Gypsum plastering(10mm)

U=0.540W/K-m2

C=3.40MJ/K

House 2SC

Cement screed (2mm)

Siporex (100mm)

Cement screed (2mm)

U=0.984W/K-m2

C=6.11MJ/K

Plaster dense (15mm)

Siporex (100mm)

Plaster dense (15mm)

U=0.932W/K-m2

C=9.49MJ/K

House 3SP

Plaster dense (15mm)

Breeze block (200mm)

Plaster dense (15mm)

U=1.44W/K-m2

C=23.6MJ/K

House 4GB

Plaster dense (15mm)

Brick inner (120mm)

Plaster dense (15mm)

U=2.31W/K-m2

C=22.2MJ/K

Concrete (heavy) (150mm)

U=3.48W/K-m2

C=20.7MJ/K

House 6CN

House

5BK

Fig. 3. The composition of the partition assembly for different houses 1IN, 2SC, 3SP, 4GB, 5BK, and 6CN. Heat capacity (C) and U value are given for

each partition.

M. Bojic et al. / Building and Environment 42 (2007) 1644–1653 1649

value, and net saving during the building life cycle arecalculated based on the current Serbian parameters foreconomic calculation: unit partition costs, unit radiatorcosts, unit district-heating costs, discount rate, escalationrate of district-heating price, and expected house life. Thissection would summarize the predicted results, whichshow how the yearly heating load, radiator power,investment cost in partitions, investment cost in radiators,investment cost in both partitions and radiators, drop inthe investment cost in both partitions and radiators, dropin costs for heating during the building life cycle, and netsaving would be affected by the type of construction usedfor house partitions.

4.1. Yearly heat load

Yearly heat load was calculated by

Q ¼ ZX8760I¼1

XN

J¼1

QI ;J . (1)

In this equation, QI,J stands for the heat load (an outputof HTB2) of room J during hourly time interval I whereI ¼ 1,y,8760 and J ¼ 1,y,N. Here, N stands for the totalnumber of heated rooms. When N ¼ NB, Q is calculatedfor all rooms in the entire house, where NB stands for thenumber of heated rooms in the entire house. WhenN ¼ N1, then Q is calculated for all rooms in the flat atthe first story, where N1 stands for the number of heatedrooms in this flat. When N ¼ N2, Q is calculated for allrooms in the flat at the second story, where N2 stands forthe number of heated rooms in this flat. Q is practically

proportional to the yearly consumption of primary fuel(this is coal for this case) and yearly CO2 production, whichis a measure of the global environmental performance ofthis house.In Fig. 4, the yearly heat load is given for each house.

The values are given for entire house, flat at the first story,and flat at the second story.For entire houses, it was found from Fig. 4 that the

yearly heat load depends on the type of partitions. Forthe house with concrete partitions, the yearly heatload has the maximum value of 8.78MWh. Then, forhouse with glass-wool partitions, the yearly heat load hasthe minimum value (around 4% lower) of 8.47MWh. Inaddition, for both the houses with siporex partitions, theyearly heat load also has a low value of 8.54MWh. Inconclusion, the maximum yearly heat load is recorded forthe house with concrete partitions and the minimum for thehouse with glass-wool partitions. Similar conclusions canbe attained for both the flats.The heat consumption of houses depends on values of

the heat capacity and overall U value of partitions. Thiscan be discussed by using Figs. 3 and 4. These figures revealthe following facts. First, houses generally consume lessheat when they have partitions with either lower heatcapacity or lower overall U value. Second, the house withconcrete partitions (with the maximum value of the yearlyheat load) would have the maximum value of overall U

value of 3.48W/Km2 (around 15% higher than theminimum overall U value encountered for these houses).Third, the house with brick partitions would have lowervalues of the yearly heat load and overall U, and slightlyhigher value of the heat capacity than those of the house

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Fig. 4. Heat consumption (Q) for houses with different types of partitions. Q is given for entire house and both the flats.

Fig. 5. Power of radiators (D) for houses with different types of partition.

D is given for the entire house and both the flats.

M. Bojic et al. / Building and Environment 42 (2007) 1644–16531650

with concrete partitions. Fourth, the house with breeze-block partitions would have lower value of the yearly heatload and overall U and slightly higher value of the heatcapacity than those of the house with brick partitions.Fifth, the house with breeze-block partitions would havethe maximum heat capacity of 23MJ/kg (16% higher thanthe minimum value of the heat capacity encountered forthese houses). Sixth, the house with breeze-block partitionswould have lower values of the yearly heat load, overall U,and heat capacity than those of the house with siporexpartitions using outer plaster layers. Seventh, the housewith siporex partitions using outer plaster layers wouldhave lower values of the yearly heat load and heat capacity,and slightly higher overall U value than those of the housewith siporex partitions using outer cement layers. Eighth,the house with glass-wool partitions would have lowervalue of the yearly heat load, overall U, and heat capacitythan those of the house with siporex partitions using outercement layers. Ninth, the house with glass-wool partitions(with the minimum value of the yearly heat load) wouldhave the minimum heat capacity of 3.4MJ/kg, theminimum overall U value of 0.54W/Km2. In conclusion,although houses with lower overall U value and heatcapacity will generally consume less heat, there are twospecial situations that may also yield a decrease in theyearly heat load: (1) increase in the heat capacity when adecrease in overall U value is required and (2) increase inoverall U value when an decrease in the heat capacity isrequired.

4.2. Power of radiators

Power of radiators (D) for houses with different types ofpartition is given in Fig. 5 for the entire house and both theflats. D represents sum of the maximum values among the

predicted hourly heating loads in the entire year for eachheated room,

D ¼XN

J¼1

Qmax;J . (2)

Here, Qmax,J ¼ max(QI,J) where I ¼ 1,y, 8760. Higherpower of radiators would mean their bigger size, highercapacity of the heat plant (that generates their heat), theirhigher embodied energy, and higher embodied energy ofthe heat plant. Then, the environmental performance of thehouse and flats should, therefore, be regarded as poor ashigher embodied energy may yield higher CO2 production.For the entire house, it was found that the radiator

power depends on the type of partitions. For the housewith brick partitions, the radiator power has the minimumvalue of 14.6 kW. For the house with glass-wool partitions,the radiator power has the maximum value of 15.4 kW (6%higher). In conclusion, the highest radiator power is

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Fig. 6. Investment costs for houses with different types of partitions. Investment costs are given for partitions (IP), heaters (IR), and both partitions and

heaters (IT). IT6CN�IT represents a drop in IT relative to that for the house with concrete partitions.

M. Bojic et al. / Building and Environment 42 (2007) 1644–1653 1651

recorded for the house with glass-wool partitions and thelowest for the house with brick partitions. The same is validfor both the flats.

4.3. Costs for investment

The investment costs in partitions (IP), in radiators (ID),and in both partitions and radiators (IT), and drop in ITare shown in Fig. 6 for some house. Variable IP is given as

IP ¼ Atp, (3)

where A ¼ 100:7m2 represents size of partitions in aninvestigated house and tp represents cost of m

2 of partitionin present value h. Variable ID is given as

ID ¼ Dtd, (4)

where td represents the cost (in present value h) of heaterthat provides 1W of heating power. Currently, for heatersmade from aluminum, td ¼ 0:117 (present value h/W).Variable IT is given as

IT ¼ IPþ ID. (5)

It was found that the investment cost in partitions varieswith type of partitions applied in some house. For thehouse with siporex partitions using outer cement layers, theinvestment cost in partitions has the minimum of 1670present value h. For the house with concrete partitions, theinvestment cost in partitions has the maximum of 2840present value h (around 70% higher). In addition, for thehouse with glass-wool partitions, the investment cost inpartitions has a low 2290 present value h. In conclusion,the maximum investment cost in partitions is recorded forthe house with concrete partitions and the minimum for thehouse with siporex partitions using outer cement layers.

It was found that the investment cost in radiators varieswith type of partitions applied in some house. For thehouse with brick partitions, the investment cost in

radiators has the minimum of 1700 present value h. Forthe house with glass-wool partitions, the investment cost inradiators has the maximum of 1796 present value h

(around 6% higher). In conclusion, the maximum invest-ment cost in radiators is recorded for the house with glass-wool partitions and the minimum for the house with brickpartitions.It was found that the investment cost in both partitions

and radiators varies with type of partitions applied in somehouse. For the house with siporex partitions using outercement layers, the investment cost in both partitions andradiators has the minimum of 3386 present value h. For thehouse with concrete partitions, the investment cost in bothpartitions and radiators has the maximum IT6CN ¼ 4553present value h (around 34% higher). In addition, for thehouse with glass-wool partitions, the investment cost inboth partitions and radiators has low 4086 present value h.In conclusion, the maximum investment cost in bothpartitions and radiators is recorded for the house withconcrete partitions and the minimum for the house withsiporex partitions using outer cement layers.For some house, the drop in its value of the investment

cost in both partitions and radiators from that of IT6CN

varies with type of partitions applied in some house. Forthe house with siporex partitions using outer cement layers,this drop has the maximum of 1033 present value h. Inaddition, for houses 3SP and 1IN, the drop has somewhatlower 406 and 374 present values h, respectively. Inconclusion, the maximum drop is recorded for the housewith siporex partitions using outer cement layers.

4.4. Costs for heating

The drop in the costs for heating is shown in Fig. 7. Costfor heating during the building life cycle is calculatedduring entire house life (n years) in money units of the firstinvestment year (present value h by using the following

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Fig. 7. The drop in costs for heating (CQ6CN�CQ) and net savings for the investigated houses.

M. Bojic et al. / Building and Environment 42 (2007) 1644–16531652

equation after Fuller and Petersen [12]:

CQ ¼ Qtqð1þ eÞ

ðd � eÞ1�

1þ e

1þ d

� �n� �. (6)

Here, tq represents district-heating cost in present value hof MWh of heat, d stands for the discount rate, e stands forescalation rate of district-heating price, and n stands for theexpected house life. Currently for Serbia, tq ¼ 18:5 presentvalue h/MWh, d ¼ 0:1226, e ¼ 0:1, and n ¼ 100 years.Values of of d and e are taken here to be constant duringthe entire useful life of a house. However, due to currentfluent economic situation in Serbia, these values may bevariable.

For some house, the drop in a value of the cost forheating during the building life cycle from that of CQ6CN

varies with the type of partitions applied. Here, CQ6CN

represents the maximum value of the cost for heatingduring the building life cycle (recorded for the house withconcrete partitions). The maximum drop of 12,889 presentvalue h is recorded for the house with glass-wool partitions.Lower cost for heating is obtained due to use of partitionsof types other than 6CN.

4.5. Net-saving analysis

For all investigated houses, the net saving given in Fig. 7is calculated after Fuller and Petersen [12] as

NS ¼ LCC6CN � LCC ¼ ðCQ6CN � CQÞ þ ðIT6CN � ITÞ.

(7)

Here, LCC stands for the life-cycle costs for some houseand LCC6CN for the life-cycle costs for the base house (thehouse with concrete partitions). LCC represents sum of thefollowing costs (in the present value h) incurred by somehouse during its life: the investment cost in both partitionsand radiators, other initial investment costs, the cost forheating during the building life cycle, other operating costs,

capital replacement costs, residual value, repair costs, andmaintenance costs. It is assumed that only the cost forheating during the building life cycle and investment cost inboth partitions and radiators are different for theinvestigated houses, while all other costs are the same.This is the reason that net saving for some house iscalculated as sum of its drop in the cost for heating duringthe building life cycle and in the investment cost in bothpartitions and radiators. Here, the house with concretepartitions is taken as the base house because it has themaximum value of the life-cycle cost (the maximum valueof CQ+IT) among all the investigated houses.It was found that the net saving for investigated houses is

not the same. The maximum net saving of around 13,300present value h is recorded for the house with glass-woolpartitions. Somewhat lower life-cycle cost of around 11,900h is found for the house with siporex partitions using outercement layers. In conclusion, the maximum net saving isrecorded for the house with glass-wool partitions.

5. Conclusion

For typical small house in Serbia, we simulated how itsheating depends on applied type of partitions inside thehouse. The following was found. First, the house withpartitions of thermal insulation has the minimum values ofthe yearly heat load and cost for heating during thebuilding life cycle. Its values of the yearly heat load andcost for heating during the building life cycle are 4% lowerthan that for the house with maximum values of the yearlyheat load and cost for heating during the building life cyclewhen partitions are made of concrete. Second, the housewith glass-wool partitions has the maximum values of theradiator power and investment cost in radiators. Thesevalues are 6% higher than their minimum values for thehouse with brick partitions. Third, the house with siporexpartitions using outer cement layers will have the minimum

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value of the investment cost in partitions. This value is70% lower than the maximum value recorded for thehouse with concrete partitions. Fourth, the maximumvalue of (CQ6CN�CQ) ¼ 12,889 present value h is foundfor the house with thermal insulation partitions. Fifth, themaximum value of NS ¼ 13,300 present value h is foundfor the house with thermal insulation partitions and thelowest of NS ¼ 0 was found for the house with concretepartitions. Finally, based on these overall investigations,we may recommend that our house have partitions mademainly from thermal insulation because the house annuallyconsumes the minimum amount of heat and has themaximum value of net saving during years of its useful life.In addition we may recommend that for design of otherhouses, architects do similar energy and economic analysesand select adequate type of partitions.

These research efforts will be extended in future to covermultitude of interesting issues. Then, we should investigatehow the selection of adequate partitions in some house isinfluenced by (1) application of other heating systems inthese buildings, (2) application of different temperaturesettings inside these houses (such as uniform temperaturesetting throughout the structure), (3) application of theenvelope with better or worse thermal performances, (4)application of different usage schedules, and (5) uncertain-ties in investment and energy costs.

References

[1] MMERS. Draft of energy law, Retrieved August 20, 2003, from

Ministry of Mining and Energy of Republic of Serbia (MMERS).

2003. WEB site http://www.mem.sr.gov.yu

[2] MSTDRS. National program of energy efficiency, Retrieved

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