Life cycle cost analysis
The financial calculation was carried out according to the Global Cost method described in the European Standard EN 15459 and was provided for economic issues of building systems involved in the energy demands . This standard permits that only components and systems which influence the energy performance of the building are considered and others could be assumed constants and not be applied in the calculations . Global cost is sum of the present value of the initial investment costs , energy costs , maintenance costs , operational costs and replacement costs ( referring to the starting year ), as well as disposal costs and its equation can be written as
( 1 )
Where : τ : calculation period
C g
( τ ): global cost referred to the starting year τ0
C I
: initial investment cost
C a , i
( j ): annual cost for component j at the year i
R d
( i ): discount factor for the year i
V f , τ
( j ): final value of component j at the end of calculation period Calculation period was considered 30 years , as recommended for residential buildings in EN 15459 . Annex A of the same standard represents life span of construction elements which is determining in calculation of their replacement cost and residual value as well as their maintenance costs which is a percentage of initial cost .
Financial input parameters
Energy carriers of the building is considered to be gas and electricity as it is common among Italian residential buildings and their costs are obtained through the energy tariffs provided by AEEG ( Authority of electricity and gas ) and are updated every three months . According to AEEG databank updated on December 2014 , electricity and gas prices are considered to be 0.2716 €/ Kwh + VAT ( 10 %) + excise costs and 0.4759 €/ m3 + VAT ( 22 %), respectively . It must be noted that in this study illumination related costs as well as energy consumption of household devices are not considered . Historical data from ISTAT ( Italian national institute of statistics ) and ECB ( European Central Bank ) are utilized as data resources of interest rate and inflation rate . Rate of development of energy price is another important parameter which affects total global cost by altering energy cost and differs from inflation rate ; data sources for its estimation were taken from AEEG as well as Italian stock market and European commission reports . Moreover product market might vary from region to region inside the country and cause differences in final investment cost rather than the assumed costs . To consider this into calculations , investment costs are taken as uncertain values and accordingly wall envelope related prices in various geographical locations of Italy were studied to be compared and estimate the variation of products price . According to Burhenne ( Burhenne , Tsvetkova , Jacob , Henze , & Wagner 2013:143 – 154 ), input uncertainty and future trend of economic data are determined by measurements , estimates , and judgements . In this study , ARIMA models were utilized to analyze historical data to predict averages for future values based on time series data ; Predictions obtained by the models are also subject to uncertainties , therefore a plausible variation range of values are provided by means of given confidence interval of 90 %. Rate values and variation interval of parameters considered in calculations are represented in Table 4 .
80 ZEMCH 2015 | International Conference | Bari - Lecce , Italy