Determining Optimum Insulation Thickness of a Building Wall using an

7th International Exergy, Energy and Environment Symposium

Determining Optimum Insulation Thickness of a Building Wall using an Environmental Impact Approach 1*

1

Özel Gülcan, 1 Açıkkalp Emin, 2 Karakoc T. Hikmet, 3 Hepbasli Arif, 4 Aydın Ahmet

Bilecik S.E. University, Engineering Faculty, Department of Mechanical and Manufacturing Engineering, Bilecik, Turkey 2 Anadolu University, Faculty of Aeronautics and Astronautics, Department of Airframe and Powerplant Maintenance, Eskisehir, Turkey 3 Yasar University, Faculty of Engineering, Department of Energy Systems Engineering, Izmir, Turkey 4 Sakarya University, Faculty of Engineering, Department of Mechanical Engineering, Sakarya, Turkey * E-mail: [email protected]

Keywords: Thermal insulation, building wall, environmental impact Abstract This study investigates optimum insulation thickness of a building wall in the city of Bilecik, Turkey. The optimum insulation thicknesses are determined using the life cycle cost analyses and a novel method based on the environmental impact analysis. Two different insulation materials, rockwool and polystyrene, are considered in the analyses. In this regard, the fuel consumption, the CO2 emission and the environmental impacts of the system related to energy loss are determined first. Next within the life cycle cost (LCC) analysis, insulation cost, the fuel cost and the total cost are calculated. The results for the environmental impact of the system, the net environmental saving, the fuel consumption, the CO2 emission and the total cost according to the insulation thickness are then given. The optimum insulation thickness calculated by environmental impact analysis and LCC analysis are compared. Finally, the main concluding remarks are listed while the recommendations are made.

I. Introduction

investigated all the parameters affecting the optimum thermal insulation thickness for building walls was carried out by Kaynakli (2011). He used an economic model based on the life-cycle cost analysis to determine the optimum insulation thicknesses. Bolattuk (2008) investigated the optimum insulation thickness for the external walls of buildings with respect to cooling and heating degree-hours in the warmest zone of Turkey. He calculated that the optimum insulation thickness varies between 3.2-3.8 cm depending on the cooling degree-hours and 1.6 and 2.7 cm for the heating loads. Effect of the fuel type, wall configuration and combustion paremetres on optimum insulation thickness was determined by Arslan et al. (2010). He calculated optimum insulation thicknesses between 0.291 m and 0.1352 m depending on the fuel types, wall types, and combustion parameters. Environmental impact obtained from the LCA is combined with exergy analysis and it is called as exergoenvironmental analysis. This new method is used for the calculating environmental impact of the energy conversion systems (Meyer et al., 2009; Tsatsaronis, 2008). Environmental impacts of the several materials are associated with points and listed in the ECO indicator 95 and ECO indicator 99 (Goedkoop et al., 2000; Goedkoop, 1995).

In the world, environmental problems have become widespread along with the population growth, energy consumption and the industrialization (Dinçer, 1999). At the present time, the most important indicator of the environmental problems is the global warming. Gases (Carbon dioxide, Methane, Nitrous oxide and Fluorinated gases) that trap heat in the atmosphere are called greenhouse gases (United States EPA, 2014) Carbon dioxide which is the output of the energy conversion process has largest effect on the global warming by the rate of 81% (Karakoc et al., 2011). The effects of the global warming have reached the sensible levels and environmental impact analysis has gained a greater importance for the energy policies of the countries. In Turkey, buildings are responsible of 30% of the total green gas emissions (Karakoc et al., 2011). In order to decrease CO2 emissions and fuel consumption, energy losses from the building must be minimized. Thermal insulation is an important, applicable and rational solution to achieve this aim by altering properties of building envelopes. In addition to this, thermal insulation provides the cost savings and thermal comfort (Ekici, 2011).

In this study, to determine the optimum insulation thickness, a novel method based on the environmental impact analysis is performed to an external building wall. In our analysis, the rockwool and polystyrene are used as the insulation material. LCC analysis is commonly used in studies mentioned above for evaluating the optimum insulation thickness. LCC analysis is applied for the investigated wall and the results of LLC and environmental analysis are compared.

Many studies have been performed on the optimum insulation thickness in the literature (Hasan, 1999; Bolattürk, 2006; Sisman et al., 2007; Yıldız et al., 2008; Yu et al., 2008; Kaynakli, 2008). These studies determine optimum thickness using energy, exergy, economic and emissions methods. Ucar et al. (2010, 2011) determined optimum insulation thickness by using exergy based analysis methods for the different climatic regions and fuels. A parametric study

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b

: Environmental impact point (mPts/kg) : Total environmental impact of the system B (mPts/m2-year) E Annual energy (J/ m2-year) : Convection heat transfer coefficient h (W/m2.K) Hu : Heating value (J/kg) HDD : Annual heating degree day (oC.day) k : Thermal conductivity (W/m.K) L : Thickness of the wall component (m) m : Annual fuel mass (kg/m2-year) q : The annual heating loss (J/m2-year) R : Thermal resistance (m2.K/W) : Annual net saving of environmental impact S (mPts/ m2-year) SE : Annual net saving of energy loss (J/ m2-year) T : Temperature (oC or K) U : Heat transfer coefficient (W/ m2.K) V : Volume (m3) x : Insulation thickness (m)

Fig. 1: Investigated building wall system.

The annual heating loss (J/m2-year), from the unit area of the wall is determined from equation (1) by the way of heating degree-day (Başogul, 2011):

Greek letters η : Efficiency of the heating system (%) ϕ : Chemical exergy factor of the fuel ρ : Density (kg/m3)

q = 86400 HDDU

Subscripts br : Brick CO2 : Carbon dioxide c : Cost en : Environmental F : Fuel i : Inside air ip : Inside plaster ener : Inside air ins : Insulation Loss : Loss o : Outside air op : Outside plaster nins : No-insulation T : Total

(1)

where HDD is the heating degree-days (oC.day) and U is the heat transfer coefficient (W/m2K). Heat transfer coefficients (W/m2K) for no-insulation and the insulated wall conditions can be calculated using equation (2) and (3) respectively:

U nins =

U ins =

1 1 = Ri + Rip + Rbr + Rop + Ro RT , nins

(2)

1 1 = Ri + Rip + Rbr + Rins + Rop + Ro RT ,ins

(3)

RT ,nins is the total thermal resistance of the wall without the insulation material, which is

II. Modelling and analysis II.1.Environmental impact analysis

RT , nins =

A composite wall investigated in this study is presented schematically in Fig. 1. The building wall consists of parallel layers of inside plaster, brick, insulation material and outside plaster. Rockwool and polystyrene are chosen as the insulation material in the calculations. Some properties of the building wall components are given in Table 1. Temperatures of the outside and inside air are assumed at constant To and Ti. Natural gas is used as fuel for the heating system operated in 90% efficiency. Calculations are made annually for unit area of an external building wall.

1 Lip Lbr Lop 1 + + + + hi kip kbr kop ho

(4)

where hi and ho, is the convection heat transfer coefficients on the inside and outside of the wall. L and k are the thickness and the thermal conductivity of the wall components, respectively. Subscripts ip, br and op denotes the inside plaster, brick and outside plaster, respectively. Also RT ,ins is the total thermal resistance of the insulated wall and it is defined as follow:

RT , nins = RT ,ins +

x kins

(5)

where x and kins are the thickness and the thermal conductivity of the insulation material, respectively.

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Annual energy (J/m2-year) need from the unit area of the wall is calculated by using efficiency of the heating system ( η ) and the annual heating loss (q):

E=

86400HDDU

xen = − kins RT ,nins + 487.44

Annual fuel consumption (kg/m2-year) depending on the annual energy need is determined using the equation (7). mF =

86400 HDDU Hu η

Inside plaster Brick İnsulation material - Rockwool - Polystyrene Ourside Plaster

0.02 0.19

0.87 0.45

0-0.4 0-0.4 0.03

0.04 0.032 0.87

2

The net saving of energy loss from the pipe surface (J.K/m) is:

SE = Enins − Eins

Life cycle cost analysis is an economic evaluation method that determines the total cost of system components over a period of time. For a building wall LCC analysis is used to determine the optimum insulation thickness in order to take into account the change in interest and inflation (Ucar, 2010). The annual fuel cost per unit area is: cF = c f mF

From this equation, CO2 emission (kg/m2-year) can be given as equation (8).

mCO

2

(13)

where is the cost of fuel. The fuel cost over a lifetime is calculated using the present worth factor (PWF), in the life cycle cost. The PWF depends on the inflation rate, g, and interest rate, i, and is adjusted for inflation as (Ekici, 2012) i − g 1 + g ; i > g * i = (14) g −i ; i < g  1 + i and then PWF is defined as follows (Arslan, 2010)

CO2 + 2 H2O + 7.52 N2

 86400 HDDU  = 2.75   Hu η  

(12)

II.1.Life cycle cost analysis

Combustion equation can be written as follows: CH4 + 2 (O2 + 3.76 N2)

(11)

2

Tab.1: Some properties of the building wall materials (Bolattürk, 2006; Izocam, 2014)

Conductivity (W/mK)

bins Huη ρins

−(bF mF + bCO2 mCO + bins ρins xins )ins

(7)

Thickness (m)

)

+ 0.36bF HDDkins

S = (bF mF + bCO2 mCO ) nins

where Hu is lower heating value of the fuel (J/kg). More than 90 % of natural gas is composed of methane (CH4) so methane can be used in the combustion equation and the combustion process is assumed as complete to facilitate calculations.

Layer

CO2

(10) BT will receive the minimum value at the optimum insulation thickness. The net saving of the environmental impact (mPts/m2-yer) is:

(6)

η

(b

1 − (1 + i* )− N  PWF =  i* (1 + i ) −1 

(8)

Total environmental impact function of the system (Özel, 2014), BT (mPts/m2-year) is calculated from equation (9). (9) BT = bF m F + bCO2 mCO2 + bins ρ ins xins

; i≠g ; i=g

(15)

where i* is the interest rate adjusted for the inflation rate and N is the lifetime of the insulation material. Finally, the annual fuel cost can be shown as

Here, bF is the environmental impact of the fuel (mPts/kg), bCO2 is the environmental impact of CO2

CF = c f PWFmF

(mPts/kg), and bins is the environmental impact of the insulation material (mPts/kg). Also, (kg/m3) is the density of the insulation material. The optimum insulation thickness is obtained by getting the derivative of BT with respect to x and set equal to zero as follows:

(16)

The annual cost of the insulation material per unit volume can be calculated as,

Cins = ciVins

(17)

where is the cost of per m3 insulation material and is the volume of the insulation material.

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Total Environmantal Impact (mPts/m 2-year)

CT = c f PWFmF + ciVins

(18)

The annual cost saving per unit area of the wall is:

SC = CT,nins − CT ,ins

(19)

The optimum insulation thickness is obtained getting the derivative of SC with respect to x and equal to zero. SC will receive maximum value at optimum insulation thickness. Data used calculations can be seen in Tab. 2.

by set the in

1000 1000

500 500

0 0 0.0

0.2

Environmental Impact Saving (mPts/m 2-year)

The annual total cost of the building wall is:

0.4

insulation thickness (m)

xC = 293.94

CF HDDkins PWF − kins RT ,nins Cins Huη

BT(Rockwool)

(20)

Unit

Environmental impact point

mPts/kg

Value

Rockwool (Goedkoop,2000)

4.2

Polystyrene (Goedkoop,2000)

8.3

Fuel (Goedkoop,1995)

114

CO2 (Goedkoop,1995) Mean temperature for heating period(Turkish Meteorological Office) Heating degree day (Dombaycı, 2009) Boiler efficiency Density of insulation material Rockwool (Izocam, 2014) Polystyrene (Kaya et al., 2006) Lower heating value of the fuel (Arin, 2002) Fuel cost (Aksa Natural Gas, 2014) Inflation rate ( Central Bank Of The Republıc Of Turkey,2014) Interest rate ( Central Bank Of The Republıc Of Turkey,2014) Life time (N) Glass wool cost (Kaynakli et al.,2008 ) Rock wool cost (Izocam, 2014)

oC

5.45 9

oC-days

2966 0.9

kJ/kgK $/kg

0,53

As it appears in Fig. 3, application of the insulation material decreases the energy loss from the building wall. Until the environmental optimum insulation thickness, energy loss decreases significantly and after the optimum point, it decreases continues negligibly. According to this results, when rockwool and polystyrene are used at the optimum thickness, energy loss from the building wall decreases by 89% and 92%.

8,39 9,65

year $/m3 $/m3

S (Polystyrene)

It is seen from the Fig.2 that the total environmental impact of the system decreases with the insulation thickness until a certain point called as optimum point. Environmental impact of the system gets the minimum value at this point named optimum insulation thickness. The optimum insulation thicknesses for the rockwool and polystyrene are calculated as 0.232 m and 0.219 m respectively by utilizing the Equation (10). At optimum points, environmental impacts of the system are determined as 216.12 and 171.304 mPts/m2-year. The net environmental impact saving of the system tends to increase logarithmically up to the optimum insulation thickness while the total environmental impact decreases.

kg/m3 105 45 50x103

S (Rockwool)

Fig. 2: Changes of the total environmental impact and the net environmental impact saving according to the insulation thickness.

Tab. 2: Parameters used in calculations

Parameter

BT(Polystyrene)

10 75 132

III. Results and Discussion In the present study, the environmental analysis and life cycle cost analysis are applied to an external building wall in order to determine the optimum insulation thickness. Rockwool and polystyrene are chosen as the insulation material for the building wall in the city of Bilecik, Turkey. -4-


called the economical optimum point, after which it starts to increase (Fig. 6). For the rockwool and polystyrene economical optimum points are calculated as 0.065 m and 0.085 m respectively. The net cost saving of the system tends to increase logarithmically up to the optimum insulation thickness while the total cost decreases.

4.0x105

2.0x105 2.0x105

Energy Loss Saving ( kJ/m 2-year )

Energy Loss ( kJ/m 2-year )

4.0x105

80

Cins (Rockwool)

70

CF (Rockwool) Cins (Polystyrene)

60

CF (Polystyrene)

0.2

0.4

2

0.0

Cost ($/m -year)

0.0

0.0

insulation thickness (m) E (Rockwoll)

SE (Rockwoll)

E (Polystyrene)

E (Polystyrene)

Fig. 3: Effect of the insulation thickness on energy loss and energy loss saving.

30

10 0 0.0

0.1

0.2

0.3


Fig. 5: Variations of insulation and fuel cost with insulation thickness. 70

Cins (Rockwool)

Cost ($/m2-year)

Fuel Consumption & CO2 emission (kg/m2-year)

40

20

Variations of the fuel consumption and the CO2 emission versus the insulation thickness are presented in Figure 4. As insulation thickness increases, the fuel consumption and the CO2 emission decrease. Similar to the energy loss, the fuel consumption and the CO2 emission decrease logarithmically. Until the environmental optimum point, a rapid decrease on the fuel consumption and the CO2 emission is observed. The results show that for the rockwool decreasing of the no insulation condition until 0.4 m insulation thickness is 94 % for the fuel consumption and the CO2 emission. 89% of these obtain until the optimum insulation thickness. For the polystyrene decrease in the fuel consumption and the CO2 emission is 95% between no insulation condition and 0.4 m insulation thickness. 92% of these obtain until the optimum insulation thickness. mF (Rockwoll)

25

50

60

SC (Rockwool) Cins (Polystyrene)

50

SC (Polystyrene)

40 30 20

mCO2 (Rockwoll) mF (Polystyrene)

20

10

mCO2 (Polystyrene)

0

15

0.00

0.05

0.10

0.15

0.20

0.25

0.30

10

insulation thickness (m) 5

Fig. 6: Variations of total cost and cost saving with insulation thickness.

0

IV. Conclusions 0.0

0.1

0.2

0.3

0.4

In this study, optimum insulation thickness of a building wall is determined by using two different analysis method. Firstly, the environmental impact analysis based on the life cycle assessment is performed for the wall system. And then results are compared with the LCC analysis which is the most commonly used for determining the optimum insulation thickness of a bulding wall. Some concluding remarks can be summarised as follows: • For the rockwoll environmental and economical optimum insulation thicknesses


Fig. 4: Fig.4: Fuel consumption and CO2 emission versus the insulation thickness.

As a part of the LCC analysis, insulation and fuel costs are evaluated and results are presented in Fig. 5. Investigating the graphics, it can be seen that initially fuel cost decreases in larger steps up to a certain point and then decreasing steps get smaller. Insulation cost increases linearly because of it only depends on the insulation thickness. Total cost of the system decreases logarithmically until the minimum point, -5-


•

•

•

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are calculated as 0.232 and 0.065 m respectively. For the polystyrene environmental and economical optimum insulation thicknesses are calculated as 0.219 and 0.085 m respectively. For different insulation materials and wall components, optimum insulation thicknesses based on the environmental impact and LCC analysis can be calculated by using Equations (10,20) When compared two methods the optimum insulation thickness for the life cycle cost analysis is lower than environmental impact analysis.

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