Economic and environmental impacts of thermal insulation used in different duct sizes

Abstract

Keywords: Optimum Insulation Thickness; Energy Saving; Life Cycle Cost Analysis; Environmental Analysis

Introduction

Energy consumption (EC) is escalating throughout the globe due to rapid population growth, improvement in living standard and style of human beings, urbanization, and migration towards large cities and development in technologies [1]. In addition to that the scarcity of energy supply, depletion of existing energy resources and environmental annihilation has raised a concern about EC. Therefore, EC is a critical issue of recent research. Suitable energy conservation measures significantly decrease EC [2]. Generally, there are four main sectors of EC i.e. industrial, transportation, building (commercial and residential) and agriculture. The building is responsible for 40% of the total energy demand of the developed countries [3] and the HVAC system is responsible for 10-20% to maintain a suitable indoor environment [4]. It results in 40% of the total greenhouse gas emissions [5]. However, the use of insulation material in buildings and the HVAC system reduces EC significantly. In an HVAC system, energy loss due to improper use of insulation material and thickness on ducting and piping [6]. Therefore, the use of insulation in an HVAC system not only reduces its EC but also abates emission products. Mostly engineering investigations consider insulation material and thickness as an important parameter for economic and environmental savings. The economic insulation thickness concept is based on net saving obtained using insulation cost and energy cost for the HVAC system over the expected lifetime. The OIT for HVAC pipe or duct is determined using design, operating and economical parameters [7]. The degree-time concept is one of the simplest methods used to determine the cooling/heating energy requirement of a building under constant operating and environmental conditions. Zaki and Al-Turki [8] determined OIT for the pipelines of oil industry using LCC analysis. They considered superheated steam, furfural, crude oil, and 300-distillate as a working fluid and Rockwool and calcium silicate as an insulation material. The results indicate net saving increases with pipe size. Li and Chow [9] determined OIT for different size pipes to protect them from cold freezing using LCC analysis. The results reveal that insulation thickness decreases with insulation’s thermal conductivity and cost, while it increases with insulated pipe exterior surface temperature. Soponpongpipat et al. [10] estimated the OIT for HVAC duct using thermo-economic analysis. They considered galvanized steel duct (0.5 m) with This paper was recommended for publication in revised form by Regional Editor Hafiz Muhammad Ali 1 Department of Mechanical Engineering, Mehran University of Engineering & Technology, SZAB, Campus, Khairpur Mir’s, Pakistan 2 Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro, Pakistan 3 Department of Electrical Engineering, Mehran University of Engineering & Technology, Jamshoro, Pakistan *E-mail address:dileepkumar@muetkhp.edu.pk Orcid id: 0000-0001-5139-0174, 0000-0003-0139-3179, 0000-0001-7146-1275, 0000-0002-8624-6145, 0000-0002-2228-4687 Manuscript Received 26 January 2018, Accepted 07 April 2018

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glass wool and rubber as insulation material for their analysis. The results show that OIT remains constant with a convective heat transfer coefficient, contrary to ES increases. Keçebas et al. [11] estimated that the maximum ES is achieved for pipe (250 mm) and FO, whereas its lower value is determined for pipe (50 mm) and geothermal energy. Additionally, they investigated that the use of geothermal energy for chiller/boiler operation produces both environmental and economic benefits. His other study [12] investigates the effect of fuel inlet, stack gas and combustion chamber temperature and air-fuel ratio on OIT, ES and PP for different pipe sizes using energoeconomic and exergoeconomic method. The results indicate that OIT calculated using energoeconomic method was greater than exergoeconomic method. The effect of wind speed on OIT, ES, and PP for HVAC’s duct installed outside the building is estimated using LCC analysis in the city of Usak, Turkey. The analysis considers LPG, NG, FO, and Coal as an energy source and Rockwool and fiberglass as insulation. The results show that the ES increases with wind speed for HVAC’s duct [13]. The above literature shows that significant research has been conducted to determine OIT, ES, and PP for pipelines installed in industries, refineries, and the HVAC system. In contrast, fewer studies are conducted for HVAC’s duct. Consequently, less attention is given towards the environmental impacts of energy loss through HVAC’s duct and piping. On the other hand, significant research has been conducted to investigate the environmental impacts of insulation used in building wall. Comakli and Yüksel [14] estimated 12.13$/m2 net energy saving and 50% reduction in CO2 emission for building wall over a lifetime of 10 years in city of Kutahya, Turkey. Dombaycı [15] estimated the environmental impacts of OIT for the exterior building wall. The analysis considered coal as a fuel and expanded polystyrene as an insulation material. He estimated that OIT reduces fuel consumption and the CO2 and SO2 emission by 46 and 41%. Yildiz et al. [16] estimated that OIT reduces CO2 emission by 30% for the insulated wall with glass wool insulation and NG, FO, coal, and LPG as a fuel. Basogul and Keçebas [17] determined the environmental impacts of OIT for district heating pipelines. The results indicate a 21% reduction in CO2 emission. Abdullah and Karameldin [18] estimated that OIT for steam piping (0.225-0.235m) reduces CO2 form 37.7-26.8 tones/m/year and SO2 from 7259 kg/m-year. In this study, the OIT, ES, PP, annual fuel consumption and emissions of CO2, CO, and SO2 for the insulated duct is determined in terms of LCC analysis. The analysis considers fiberglass as insulation material and coal, NG, LPG, FO, RH, bagasse and geothermal as an energy source. The heat conductivity and price of the insulation material, average temperature and relative humidity of conditioned air, fuel price are constant in the analysis. The results drawn from the analysis are evaluated.

Selected AIR Distribution System

The schematic view of the air distribution system for the HVAC system under study is illustrated in Fig. 1. The energy required for the chiller operation is obtained from a boiler, in which fuel sources are commonly oxidized to produce thermal energy. As for the heating coil, the supply air is directly conditioned via heat transfer between supply air and hot water. The heating coil is intended to control the relative humidity of the supply air required for the pharmaceutical zone. In the HVAC system, the conditioned air is supplied to the zone through HVAC ducts. HVAC ducts are usually made out of the galvanized steel, stainless steel and aluminum, and flexible non-metallic materials. Typical HVAC ducts are located outdoor environment, basement floors, attics, garages. There is a significant amount of energy loss occurs in an HVAC duct due to temperature difference between conditioned air and ambient air. Therefore, it is essential to insulate HVAC ducts in terms of energy-saving using different insulation materials. The design and operating parameters of the air distribution system are obtained from GSK Pharma Pvt. Ltd. are given in Tables 1 & 2. The value of density, specific heat, kinematic viscosity, Prandtl number and thermal conductivity of conditioned air inside the duct are obtained by using the appropriate mean value of operating parameters.

Analysis Of AIR Distribution System

A life cycle cost analysis considers the net saving resulting from a reduction in energy cost due to a decrease in fuel consumption with added insulation cost over the lifetime of an HVAC system. In building, the LCC analysis is

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usually used to calculate the OIT considering the effect of inflation and interest rate, maintenance cost, salvage value, operating hours, and heating value of fuel and cost of fuel and insulation material [23]. The following assumptions are considered in the analysis:

4. Fan

Figure 1. Schematic layout of simple air-distribution system

Table 1. The duct and insulation material properties [10, 13, 19] Insulation Properties Fiberglass Kins=0.037 W/m.K and Cins=352USD/m3 Galvanized Steel Kd=60.5 W/m.K, 300 ≤ dd ≤ 500 mm and 0.7 ≤ td≤ 1.006 mm Table 2. Operating parameters [13, 20-22] Parameters Value Supply air in duct Ti=293K, Pi=1kPa(g) Vi=10m/s Ambient conditions Ti=303K, Vo=4.2m/s and ho=10W/m2K CDD 2384(oC-days) Interest Rate 5% Inflation Rate 7% Lifetime 15years

The heat gain and insulation economy for an air distribution system The annual cooling loss through the HVAC duct due to heat gain from the surrounding is determined on the basis of the degree-days method [13]. 86400∙𝐶𝐶𝐶𝐶𝐶𝐶 𝑄𝑄̇𝑖𝑖𝑖𝑖 = 𝑅𝑅

where, R is the overall heat transfer coefficient of duct layers [13]. It is calculated by Eq. (2 & 3) for bared and insulated duct as shown in Fig. 2 and CDD is the cooling degree days of the city analyzed: 143

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Figure 2 exhibits a bared and insulated duct. It represents the dimension of an HVAC duct. L is the length of the duct, r1 and r2 are interior and exterior radius of the duct (r2 = r1 + td), ro is the exterior radius of an insulated duct, A1 and A2 are the interior and exterior surface area of the duct, Ao is the exterior surface area of an insulated duct. The hi and ho are convective heat transfer coefficient of conditioned air and the surrounding air. The convective heat transfer of conditioned air is calculated as

where κ_air is thermal conductivity of conditioned air, DH is a hydraulic diameter of the duct which is calculated by Eq. (5) [24] and Nusselt number (Nu) is calculated by Eq. (7 & 8) laminar and turbulent [25, 26].

where, Ac is the cross-sectional area and P is the perimeter of the duct, respectively. Reynolds Number of air flowing inside the duct is estimated as:

where, U and ϑ are the velocity and kinematic viscosity of the conditioned air. If Re ≤2800 and Pr ≤ 0.7 then flow through duct will be laminar then:

Results And Discussion

This study estimates the economic and environmental impacts of the insulation used in an HVAC duct installed outside the building in the city of Jamshoro, Pakistan. Using LCC analysis, OIT, ES and PP for different duct sizes are estimated. The analysis considers the design, operating, economic and environmental parameters given in Table 1, 2 and 3. Additionally, the environmental impacts of OIT for different duct sizes are determined using various energy sources.

Insulation thickness (m) Figure 3. Total cost verses insulation thickness

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The effects of insulation thickness on total cost, insulation cost and fuel cost over a lifetime of HVAC system is illustrated in Fig. 3. The fuel cost is inversely proportional to insulation thickness because insulation thickness over the duct reduces energy loss. Moreover, the parabolic relationship occurs between insulation thickness and cost because insulation quantity increases radially with its thickness on the duct. The total cost is the sum of fuel and insulation cost. Therefore, total cost decreases with insulation thickness up to OIT then it increases. The insulation thickness at which total cost is determined is known as OIT and it is equal to 30 mm as shown in Fig. 3. The results indicate the highest value of OIT for the duct in case NG and its lowest value in case of bagasse. The OIT for different duct sizes varies between 36.52-48.27mm for NG, 36.38-42.70mm for LPG, 18.65-24.15mm for coal, 28.79-34.64mm for FO, 16.3517.29mm for bagasse, 20.07-21.72mm for RH, 32.44-37.16mm for geothermal, respectively. The maximum value of total cost for different duct sizes under various fuel types varies between 11.93-34.98USD/m-year for NG, 10.8837.52USD/m-year for FO, 11.88-54.51USD/m-year for LPG, 6.83-22.4USD/m-year for coal, 7.67-18.72USD/m-year for geothermal, 4.49-8.91USD/m-year for bagasse and 6.79-17.19USD/m-year for RH, respectively.

Insulation thickness (m) Insulation thickness (m) Figure 4. ES V/S insulation thickness for HVAC duct considering different (a) energy source in size E and (b) sizes in case of NG The effects of insulation thickness on ES in duct size E under different energy sources are illustrated in Fig. 4. The energy-saving in duct size E increases with insulation thickness up to OIT. Once OIT is achieved further increment in insulation thickness reduces ES. Therefore, an additional increment in insulation thickness would be no longer be economical. The ES varies between 74.01-83.95% for NG, 74.02-83.91% for LPG, 54.17-70.67% for coal, 66.44-78.09% for FO, 50.25-70.49% for bagasse, 56.92-74.38% for RH, 71.03-82.87% for geothermal, respectively. The highest value of the ES is estimated for NG and LPG, whereas the lowest for bagasse. Fig. 4b shows the effects of insulation thickness in different duct sizes in the case of NG. The maximum ES occurs in Size E whereas lower value in size A. The maximum value of ES at OIT in different duct sizes for various energy sources is given in Table 4. The OIT is estimated by minimizing the Eq. 16. The outside radius of the insulated HVAC’s duct is calculated using OIT and exterior radius of the duct. Total cost is differentiated with respect to ro and equate to zero. The OIT is calculated (topt = rins - ro) using the EES optimization toolbox. The variation in PP with insulation thickness for duct size E under different energy sources is illustrated in Fig. 5a. The PP of initial investment cost occurs in duct size E decreases with insulation thickness up to OIT. Once OIT is achieved further increment in insulation thickness increases the PP. It is economically fruitless because it delays the recovery of the initial investment. The results show that the PP of initial investment for the duct size E at OIT is

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different for various energy sources. The higher value of PP corresponding to OIT is determined for bagasse and coal, whereas the lower value for NG and LPG. Other energy sources have intermediate values. Moreover, the effect of insulation thickness on PP for different duct sizes is illustrated in Fig. 5b for NG. A similar trend of variation in PP is determined for different duct sizes as shown in Fig. 5a. The higher value of PP corresponding to OIT is achieved for size A because it has higher initial investment cost and lowers fuel saving. Therefore, the lower value of PP for different duct sizes is obtained for size E. The PP for different duct sizes decrease with the size of the duct. The OIT, ES, and PP for different duct sizes at various fuels are given in Table 4. The OIT, ES, and PP vary between 16.35-48.27mm, 52.06-83.95%, and 0.204-1.005years, respectively. The higher ES in different duct sizes are obtained for NG, LPG and geothermal, whereas the lower ES is investigated for bagasse and coal and intermediate value of ES is obtained for RH and FO. The minimum value of PP for different duct sizes is obtained for NG, LPG and geothermal, its intermediate value is obtained for RH and FO, whereas, it’s higher value is obtained for bagasse and coal.

Figure 5. PP V/S insulation thickness for different (a) energy sources in size E and (b) sizes in case of NG The use of insulation material on the HVAC duct reduces heat loss. Fig. 6a exhibits the effect of insulation thickness on the annual fuel consumption of different fuel types. Fuel consumption decreases with insulation thickness. Once OIT is achieved, further increasing insulation thickness insignificantly reduces fuel consumption. The results show that fuel consumption varies between 4.2-50.12kg/m-year in the duct size E at different energy sources. The higher decrement in fuel consumption is determined in duct size E for bagasse, RH and coal, and its intermediate decrement is determined for FO whereas its lower decrement is determined for LPG, NG and geothermal. Moreover, the effect of insulation thickness on fuel consumption in different duct sizes is illustrated in Fig. 6b for NG as a fuel. The high fuel consumption decrement occurs in size A i.e. 19.52kg/m-year and size E has lower value i.e. 6.26kg/myear corresponding to OIT.

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Table 4. OIT, ES and PP for different duct sizes at various fuel types

A 48.27 16.93 19.38 37.16 42.7 30.67 21.32 74.01 50.24 54.17

Parts of air distribution system B C D 41.2 39.72 38.54 16.92 16.35 16.91 19.22 18.65 21.29 35.93 34.69 33.91 41.08 39.57 38.4 29.77 28.79 30.31 21.09 21.29 20.69 76.41 74.56 79.29 54.63 52.06 60.9 58.26 55.79 64.13

Figure 6. Fuel consumption V/S insulation thickness for different (a) energy sources in size E and (b) sizes in case of NG

Journal of Thermal Engineering, Research Article, Vol. 6, No. 1, pp. 141-156, January, 2020 (a) 500 450

Figure 7. The annual CO2 emissions versus insulation thickness (a) for different energy sources in size E and (b) sizes in case of NG Figure 7 (a and b) shows the variation in CO2 emission with insulation thickness for duct sizes and different energy sources. The use of insulation over the HVAC duct reduces fuel consumption of an HVAC system and resulting emission products. The CO2 emission decreases with insulation thickness. The higher value of CO2 emission corresponding to OIT is determined for size A and bagasse i.e. 192kg/m-year, whereas its lower value for size E and NG i.e. 11.27kg/m-year. The decrement in CO2 emission due to OIT for different duct sizes varies between 11.2334.04kg/m-year for NG, 81.81-318.33kg/m-year for bagasse, 40.73-123.43kg/m-year for coal, 14.57-50.14kg/m-year for LPG, 20.38-56.39kg/m-year and 37.04-141.59kg/m-year for RH, respectively. 80

Figure 8. The CO emissions versus insulation thickness for different (a) energy sources in size E and (b) sizes in case of NG

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Figure 9. The SO2 emissions versus insulation thickness for different (a) energy sources in size E and (b) sizes in case of coal Figures 8 and 9 exhibits the variation in CO and SO2 emission for different duct sizes with insulation thickness under different fuel types. The CO and SO2 emission decrease with insulation thickness and duct size. The CO and SO2 emission determined for size A is higher than size E. The higher value of CO emission corresponding to OIT is determined for size A and coal i.e. 59.28kg/m-year, whereas its lower value for size E and LPG i.e. 0.8kg/m-year. The decrement in CO emission due to OIT for different duct sizes varies between 3.4-10.3kg/m-year for NG, 3.6714.26kg/m-year for bagasse, 19.56-59.28kg/m-year for coal, 0.8-2.77kg/m-year for LPG, 8.21-22.72kg/m-year and 0.97-3.97kg/m-year for RH, respectively. Similarly, the higher value of SO2 emission corresponding to OIT is determined for size A and RH i.e. 0.99kg/m-year, whereas it’s lower value for size E and coal i.e. 0.15kg/m-year. The decrement in SO2 emission due to OIT for different duct sizes varies between 0.15-0.45kg/m-year for coal, 0.170.48kg/m-year and 0.25-0.99kg/m-year for RH, respectively. The percentage of fuel savings with OIT in different duct sizes is illustrated in Fig. 10. The highest value of percentage of fuel consumption reduced with OIT in different duct sizes is varying in between 36.87-40.90% in case of NG, 25.89-33.87% in case of bagasse, 28.45-33.87% in case of coal, 35.56-40.09% in case of geothermal, 36.8440.88% in case of LPG, 32.72-38.33% in case FO, 27.58-33.74% in case of RH and the total amount of fuel consumption saved is varying in between 29.24-35.98% considering all types of fuel. The percentage of emission reduction due to OIT for different parts of the air distribution system using various fuels is illustrated in Figure 11. The highest percentage of CO2 emission reduced with OIT in different parts of air distribution system is varying in between 37.74-81.1% in case of NG, 53.64-69.5% in case of bagasse, 56.84-70.81% in case of coal, 73.68-81.78% in case of LPG, 67.44-76.66% in case fuel oil, 59.36-73.2% in case of RH and the total amount of CO2 emission reduced is varying in between 58.48-71.96% considering all types of fuel. Similarly, the percentage of CO, SO2 emission reduction is estimated.

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Figure 10. Annual percentage of fuel reduction in different parts of the air distribution system

Figure 11. Percentage of emission reduction versus different fuel use in air distribution system HVAC system Note: Duct size A 300 mm, B 350 mm, C 400 mm, D 450 mm & E 500 mm.

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Conclusion

In this study, the effect of energy source and HVAC’s duct size on OIT, ES, PP are estimated using LCC analysis. This study also investigates the environmental impacts of insulation thickness on different duct sizes of an air distribution system installed outside the building in a pharmaceutical company, in the city Jamshoro, Pakistan. In this analysis, NG, LPG, coal, FO, bagasse, RH and geothermal are considered as energy sources and fiberglass as an insulation material. On the basis of the obtained results, the following conclusion is made from the present study: The OIT decreases with the duct size for various energy sources. The higher value of OIT is obtained for duct size A and NG i.e. 48.27 mm and it's lower value for duct size E and bagasse i.e. 17.40 mm. The ES values decrease with duct size. The highest value of the ES is estimated for size E and NG i.e. 83.95 whereas its lower value is obtained for Part A and bagasse i.e. 50.24%, respectively. The PP increases with the duct size. The longer value of PP is estimated for part A and bagasse i.e. 1.005year and its smallest value are 0.204year for size E and NG. The annual fuel consumption, CO2, CO and SO2 emission decrease with insulation thickness. The maximum percentage reduction in fuel consumption corresponding to OIT is around 81.8% for size A and NG and lower reduction is 51.78 for size E and bagasse, respectively. The emission of CO2, CO and SO2 vary between 53.64-81.8%, 53.62-81.76% and 49.64-76.66% for different parts and energy sources, respectively. Considering environmental impacts geothermal as an energy source is a better choice. Considering economic and environmental impacts bagasse as an energy source is a better choice.

Nomenclature

A D d h i K L 𝑚𝑚̇ N Nu Pr 𝑄𝑄̇ Re r R U V t 𝜗𝜗 f ε β f h i ins o T EC EES

Duct’s external surface area, m2 Diameter of the duct, m inflation rate, % Convective heat transfer co-efficient, W / m2 oC interest rate, % Thermal conductivity, W / m oC Length of the Duct, m Mass Flow Rate, kg/s Life time, year Nusselt Number Prandtl Number Heat gain, W Reynolds Number Radius, Thermal resistance, oC/W Velocity, m/s Volume Flow Rate (m3 /s) thickness, m Kinematic viscosity (m2/s) friction factor (-) relative roughness (-) Excess air Fuel hydraulic inlet insulation outside Total Energy Consumption Engineering Equation Solver 154

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Energy Saving Heating, Ventilation and Air Conditioning Life cycle cost Optimum insulation thickness Payback Period

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