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ARTICLE IN PRESS Renewable Energy 33 (2008) 1164–1172 www.elsevier.com/locate/renene A study on residential heating energy requirement and optimum insulation thickness O. Kaynaklià Mechanical Engineering Department, Faculty of Engineering and Architecture, University of Uludag, TR-16059 Bursa, Turkey Received 6 April 2007; accepted 5 July 2007 Available online 22 August 2007 Abstract Heat loss from buildings has a considerable share in waste of energy especially in Turkey since no or little i
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  Renewable Energy 33 (2008) 1164–1172 A study on residential heating energy requirement and optimuminsulation thickness O. Kaynakli à Mechanical Engineering Department, Faculty of Engineering and Architecture, University of Uludag, TR-16059 Bursa, Turkey Received 6 April 2007; accepted 5 July 2007Available online 22 August 2007 Abstract Heat loss from buildings has a considerable share in waste of energy especially in Turkey since no or little insulation is used in existingand new buildings. Therefore, energy savings can be obtained by determining of heat loss characteristics with using proper thickness of insulation. For this purpose, in this study, calculations of optimum insulation thickness are carried out on a prototype building in Bursaas a sample city. Considering long term and current outdoor air temperature records (from 1992 to 2005), degree-hour (DH) values arecalculated, and the variation of annual energy requirement of the building is investigated for various architectural design properties (suchas air infiltration rate, glazing type, and area). Then, the effects of the insulation thickness on the energy requirement and total cost arepresented. Based on life cycle cost (LCC) analysis, the optimum insulation thicknesses are determined for different fuel types. As aconclusion, the length of the heating period is average 221 days, and the mean heating DH value is found as 45113.2 besides changingbetween 38000 and 55000. The optimum insulation thicknesses for Bursa vary between 5.3 and 12.4cm depending on fuel types.In addition to this, the variation in Turkey is more dramatically. r 2007 Elsevier Ltd. All rights reserved. Keywords: Heating energy requirements; Degree hour; Optimum insulation thickness 1. Introduction Energy conservation has become an important part of national energy strategies and will continue growing inimportance in future, because of the fact that energy is acrucial factor for the social and economic development of societies, and energy consumption is rapidly increasing dueto the population growth, urbanization and industrializa-tion. This is particularly important for Turkey since itimports most of energy it uses. Due to the very limitedindigenous energy resources, Turkey has to import nearly55–60% of the energy from abroad to meet her needs[1,2].In general, energy consumption can be examined underfour main sectors such as industrial, building (residential),transportation and agriculture. Energy consumption in theresidential sector is one of the main parts of the totalenergy consumption in most countries. According toBuyukalaca and Bulut[3], approximately 25–30% of thetotal energy consumption in Turkey is used by theresidential sector. On the other hand, recent studies revealthat technical potential savings range 25–45% in residentialbuildings in Turkey[4]. The energy consumption of spaceheating is approximately two times more than that of theother consumption sources (such as water heating, cook-ing, food refrigeration and freezing) in residential sector.Therefore, use of proper insulation in buildings is quiteimportant for both energy savings and reducing undesir-able emissions from the burning of fossil fuels.Degree-time concept is used in many practical applica-tions such as power generation, estimation of energyrequirement—demand–consumption, plant growth andagriculture[5]. Also, variation in space heating needs canbe measured in degree-time methods using the base andoutdoor temperatures. The degree time is one of the propermethods to use in order to forecast energy consumption of residential heating[6].Satman and Yalcinkaya[6]calculated the yearly heatingand cooling degree hours (DHs) with the base temperatureof 15, 17, 18.3 1 C for heating season and with the base ARTICLE IN PRESS www.elsevier.com/locate/renene0960-1481/$-see front matter r 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.renene.2007.07.001 à Tel.: +902244429183; fax: +902244428021. E-mail address: kaynakli@uludag.edu.tr  temperature of 24, 26, 27, 30 1 C for cooling season. Theydocumented the DHs for 77 locations in Turkey. Papa-kostas and Kyriakis[7]studied on heating and coolingDHs for only 1 year at two cities in Greece. Durmayazet al.[8]calculated the residential heating energy require-ment and natural gas consumption in the city of Istanbulusing DH concept. Buyukalaca et al.[9]investigated thebase temperature effects on the heating and cooling degree-day values for Turkey. In addition, variation of the heatingand cooling degree-day was examined depend uponelevation, latitude and longitude. They found that theheating and cooling degree-day exhibit big fluctuationsthroughout Turkey, and the northeastern and the innerregions of Turkey require comparatively more heatingenergy. The heating degree-day method was used toestimate the natural gas consumption by residential heatingin Turkey in the study of Sarak and Satman[10]. Theirmodel was applied on the existing, under construction andplanned natural gas pipelines.Applications of the degree-time method have beencarried out together with optimum insulation thickness inseveral studies. In the study of Bolatturk[11], the use of insulation on external walls of buildings was analyzed. Theoptimum insulation thickness, the amount of energy savedand payback period for different fuel types were calculatedusing life cycle cost (LCC) analysis. He determined thatthe optimum insulation thickness varies between 2 and17cm, energy savings between 22% and 79%, and paybackperiod between 1.3 and 4.5 years. Al-Sanea and Zedan[12]studied the effect of insulation location on the thermalperformance of building walls under steady periodicconditions.In this study, it is stated on especially two concepts,heating energy requirement and optimum insulationthickness. Bursa is chosen as a model city. Firstly, yearlyheating energy requirement for Bursa is determinedproperly by using long-term measurements. For thatreason, 14 years’ outdoor air temperature data from 1992to 2005 are used. During these years, the lengths of heatingseason and starting–ending points are determined. Then,an optimization model based on the life cycle cost analysisusing the present worth method is developed. Using theoptimization model, the optimum insulation thicknessesfor external walls of buildings are calculated for fivedifferent types of fuel, namely, natural gas, coal, fuel-oil,LPG and electricity. 2. Calculation of heating degree hours One of the methods for estimating the energy require-ments for heating purposes in a building over a specifiedperiod is the degree-time method. The method assumesthat the energy needs for a building are proportional to thedifference between the outdoor temperature and the basetemperature. The total number of heating DHs for aheating season can be calculated asDH ¼ X N  j  ¼ 1 ð T  b À T  o Þ  j  ; for ð T  o p T  b Þ  j  , (1) ARTICLE IN PRESS Nomenclature A area, m 2 ACH air exchange per hour C  cost, $ c p specific heat, Jkg À 1 K À 1 DH total number of degree hoursGAP glazing area percentage h convective heat transfer coefficient, Wm À 2 K À 1 i  inflation rate I  air exchange rates per hour, h À 1 g interest rate k  thermal conductivity, Wm À 1 K À 1 L total heat transfer coefficient, WK À 1 LCC life cycle costLHV lower heating value of fuel, Jkg À 1 , Jm À 3 ,JkWh À 1 depending on the fuel typeLT lifetime, year m fuel consumption, kg, m 3 , kWh À 1 dependingon the fuel type N  number of hoursPWF present worth factor Q annual energy requirement, J R thermal resistance, m 2 KW À 1 T  temperature, 1 C U  overall heat transfer coefficient, Wm À 2 K À 1 V  volume, m 3 x insulation thickness, m Greek letters Z heating system efficiency r density, kgm À 3 Subscripts b basebm basementc ceilingf fuelh heatingi indoor, insideins insulationo outdoor, outsideopt optimumt totalw wallwd window O. Kaynakli / Renewable Energy 33 (2008) 1164–1172 1165  where T  o and T  b are the outdoor air and the basetemperatures, N  is the number of hours providing acondition of  T  o p T  b . As it can be seen from Eq. (1), DHvalues only take on positive values. The base temperature isthe outdoor temperature below which heating is needed. Inthis study, the base temperature is taken as 18 1 C[9].The weather data being used in energy analyses deter-mine the accuracy and characteristics of results. Therefore,the database used in energy requirement calculationsshould cover a long period and depend on recent values[9]. In this study, ambient temperature (dry bulb) dataduring 14 years (from 1992 to 2005) were used to determinethe heating DHs. These data were taken from The StateMeteorological Affairs General Directorate. The meanmonthly outdoor air temperatures measured at a meteor-ology station of Bursa are given according to years inTable1. Bursa is located in the northwest of Turkey. Turkey isdivided into four climate regions which the fourth regionhas the highest DH values, and Bursa is in second climaticzone. According to ASHRAE[14], the location of Bursa is40.18 North latitude, 29.07 East longitude and 100maltitude.Variation of the daily mean outdoor air temperature, forinstance in 2005, is shown inFig. 1. This figure is used fordetermination of the start and end of the heating season. Itis observed in this figure that the beginning and end of theheating season is the 271st day (28 September) and the128th day (8 May) of the year for the base temperature of 18 1 C. It can be calculated from the given values that theheating seasons last totally 223 days. So, the heating seasontakes about 60% of the year.Variation of the DH values based on 18 1 C for Bursa areshown inFig. 2. Owing to the fact that the outsidetemperatures are low, the heating DH values are high at thebeginning and end days of the year. As there is no need forheating between the 128th and 271st days of the year, theDHs are equal to zero. The total number of DHs isestimated DH ¼ 44657.6 for the heating period in 2005 byaid of Eq. (1) andFig. 2. ARTICLE IN PRESS Table 1The mean monthly outdoor air temperatures[13]Year January February March April May June July August September October November December1992 2.5 1.1 7.1 12.6 15.1 21.9 22.0 25.1 19.0 18.8 8.8 3.71993 3.3 3.3 7.3 11.8 15.9 21.8 23.5 24.3 19.7 16.7 8.9 8.71994 7.5 6.2 9.2 15.3 19.0 21.5 24.9 25.3 24.3 18.4 9.1 5.41995 6.4 8.2 9.1 12.2 18.4 24.2 24.5 24.1 20.6 13.8 7.6 8.21996 3.7 6.4 5.3 9.9 19.7 22.2 25.0 24.6 19.5 13.7 11.0 10.31997 5.9 4.3 6.1 9.7 18.1 22.3 24.5 21.8 17.4 14.8 10.6 7.51998 5.4 6.5 6.0 15.4 17.1 22.4 25.1 25.6 20.4 15.8 11.6 6.81999 6.8 6.5 8.9 14.5 19.0 22.9 26.1 25.4 20.9 16.1 10.9 10.12000 2.2 5.4 7.1 14.8 18.0 21.7 26.2 24.5 20.5 14.6 12.2 7.82001 7.9 7.6 14.4 14.1 17.7 23.0 27.0 25.7 21.3 16.2 10.4 5.02002 3.2 9.1 10.3 11.7 17.5 23.0 26.8 24.7 20.8 15.6 10.8 5.02003 8.9 2.8 4.6 9.9 18.8 23.8 25.3 25.6 19.2 16.6 10.0 6.32004 5.0 5.1 9.4 13.1 17.6 22.7 24.7 23.8 20.4 16.7 10.1 6.32005 6.2 6.6 8.5 14.0 17.9 21.6 24.9 25.4 20.4 13.2 9.3 8.0Fig. 1. Variation of the daily mean outdoor air temperature in 2005.Fig. 2. Variation of the degree hours in 2005. O. Kaynakli / Renewable Energy 33 (2008) 1164–1172 1166  For other years, the starting and ending days of theheating period are presented inTable 2. It is observedfrom the table that the lengths of heating period varybetween 206 and 239 days depending on years. Theheating period lasts average 7.5 months (221 days) in theall observed years. It is also seen from the table thatwhereas the earliest beginning (at 267th day) and the lastfinishing (at 146th day) years of heating season are theyears of 1995 and 1992, respectively, the longest heatingoccurs in the year of 1997. The length of heating seasonfor 1997 is 239 days, which covers 65% of the year. Forthis reason, it can be expected that the DH value for 1997is greater than that for other years. But, the year that hasthe highest DH is 1992 (seeFig. 3). Even if the longestheating season is for 1997, as it is seen inFig. 3, the yearthat requires the highest heating energy is 1992 with55272 DHs. Because of this, a year that has the longestheating period does not mean that it needs the highestheating energy requirement. It is also seen inFig. 3thatthe DH values vary in a wide range, from 38023 to 55272,according to years. Therefore, in building energy simula-tions, it should not be decided for only one or severalyears, it needs to be examined in long period and withrecent values. 3. Calculation of heating cost and optimum insulationthickness 3.1. Energy requirement and heating cost Heat losses occur in buildings mainly from externalwalls, ceiling, windows, basement and by infiltration.Physical and thermal properties for the examined building,the parameters used in the calculations and their corre-sponding values are given inTable 3. With the numericalvalues given inTable 3, overall heat transfer coefficients forthe ceiling, basement, and outside walls of the building canbe computed.In this study, the outside dimensions, width  depth  height, of the prototype building are considered as15  12  3m. It is assumed that the seasonal average airexchange rates per hour due to the ventilation andinfiltration for the example building may be I  ¼ 0.5, 1.0,1.5 and 2.0 ACH[8]. The roof, outside walls and floorareas follow 180, 162, 180m 2 , and the total volume of thebuilding is V  ¼ 540m 3 . In addition to this, the glazing area( A wd ) may be 20% (32.4m 2 ), 30% (48.6m 2 ), 40% (64.8m 2 )and 50% (81.0m 2 ) of the total outside wall area.In general, stones, concrete with reinforced iron bars,concrete bricks and clay bricks are used in the walls of thebuildings. Wall structures vary with climate. In coldclimates, sandwich walls are used. The sandwich wallconsists of an insulation layer in the middle of the twobrick layers and two plaster layers on the inside and outsidesurfaces. One of the commonly used for insulationmaterials is polystyrene[15]. Hence, in this study,polystyrene is chosen for the insulation of the outsidewalls. The insulation materials for ceiling and basement aretaken as fiberglass and rock wool, the properties of whichare given inTable 3[16–18]. The total heat transfer coefficient ( L ) of the prototypebuilding can be calculated as L ¼ X M i  ¼ 1 UA þ I  ð r c p Þ air V  = 3600, (2)where M  represents the zones where the heat losses takeplace (i.e. outside walls, windows, ceiling, and basement).( r c p ) air is the volumetric thermal capacity of air, and it istaken as 1200Jm À 3 K À 1 [14]. Hence the term of  L isrewritten as L ¼ U  o ; w ð 162 À A wd Þþ U  wd A wd þ U  bm A bm þ U  c A c þ IV  = 3. (3) ARTICLE IN PRESS Table 2The starting and ending days of heating period for each yearYears Heating season (Julian days) Length (days)1992 1–146, 281–366 2321993 1–138, 274–365 2301994 1–128, 287–365 2071995 1–126, 267–365 2251996 1–134, 272–366 2291997 1–140, 267–365 2391998 1–133, 282–365 2171999 1–125, 277–365 2142000 1–129, 279–366 2172001 1–120, 280–365 2062002 1–127, 282–365 2112003 1–138, 277–365 2272004 1–132, 279–366 2192005 1–128, 271–365 223Mean average 1–132, 277–365 221Fig. 3. Variation of the degree hours with years. O. Kaynakli / Renewable Energy 33 (2008) 1164–1172 1167
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