A LIFE-CYCLE COST ANALYSIS OF THE PASSIVE HOUSE
“POLITEHNICA” FROM BUCHAREST
The objective of this article is to create a mathematical model based on the
analysis of the life cycle cost of a passive house, including its technical design
variations. In this study we analyzed 14 types of houses derived from the design of the
passive house POLITEHNICA; every house was differentiated by the type of
renewable solution used (EAHX, GHP, solar collectors, PV panels) or by the
insulation thickness, and it was compared with H12, a standard house with classical
HVAC systems and a thermal insulation of 100 mm. The houses were compared
according to criteria of economic performance throughtout their life cycle. It was
found that the additional investment in an energy efficient house can be recovered in
16-26 years, 9-16 years and 16-28 years if the replaced HVAC system is classical gas
fuelled, electric or District distribution. A sensitivity analysis is performed which
revealed the influence of the price of electricity and PV panels. The classification
system made the decision-making process easier for a possible investment in a
solution. This classification system showed that the first three recommended solutions
for investment are the houses H14, H17 and H20.
Keywords: Life-Cycle Cost Analysis, Passive House, Economic Efficiency
Nomenclature
AIRR- Adjusted Internal Rate of Return, [-];
C- Cost [Euro];
ce- unit cost of electric energy, Euro/kWh];
Ce(i)- total cost of the energy in the year i, [Euro];
DPBT- Discounted Payback Time, [Years];
E, Eel, Ei, i=P,S,PHI,PV_HVAC,PV_Storage,N,Grid_balance- total energy, electric energy, energy: primary,
secondary, PassivHaus Institut recommended, PV delivered to HVAC sistem, PV delivered to
storage tank, total delivered by PV, electric network (grid), grid electric balance; [kWh/m2/y];
fgrid- index of bi-directional interaction building-network;
fP-S- Factor of transformation from primary to secondary energy, [-];
FV- Future value, [Euro];
fs- factor of variation of the escalation of the prices from sensitivity analysis;
I0- initial investment, [Euro];
INT()- integer function;
Inv- Investment [Euro];
LCC, LCCbasa case, LCCalternative - Life-Cycle Cost: standard, basic project, alternative project, [Euro];
NS- Net Saving, [Euro];
PV, PVxi- Photovoltaic panels; Photovoltaic panels multiplied by i factor of level of production
PVi, i=Invest,Struct,Ins,NonReimburs,Energy,Subsid,Repl,OM&R,Pers,Taxes,Envir,Residual,Decommis- Present value: investment,
basic structure, insulation, non-reimburs funds of investment, energy, subsidies, replacements,
Operation Maintanance and Repair, Personnel, Taxes, Environmental taxes, Residual cost,
Decommisioning cost;
Qi, i=H,C,walls,fen,solar,vent&leak,int,ground,DHW,P,S,SC,EAHX,GHP - Thermal load: heating, cooling, walls,
fenestrations, solar radiation, ventilation and air leakage, ground, Domestic Hot Water, primary,
secondary, solar collector, EAHX heat exchanger,
ra, ri, rrd, rre, rre,s- rate of actualization, rate of inflation, real rate of discount (interest), real rate of
escalation (of prices), real rate of escalation (of prices) of the sensitivity analysis;
ROOT()- root function;
SIR- Saving-to-Investment Ratio, [-];
1. Introduction
Energy efficient houses began to be widely publicized after the oil crisis of
the 1970s that led to an alarming increase in energy prices.This led to the
development of concepts related to super-insulation, air tightness of the building,
passive design and also the implementation of high efficiency heat recovery. The
passive solar design for buildings was promoted by G. F. Keck with the "House of
Tomorrow" (1933) and by MIT University with "Solar House 1" (1939) and later,
the houses of the 1970s such as "Philips Experimental House" (Germany, 1975),
"DTH Zero-Energy House" (Denmark, 1975), "Lo-Cal House" (USA, 1976), "The
Saskatchewan Conservation House" (Canada, 1977), "Leger House" (USA, 1977)
brought to the forefront issues such as super-insulation "super-glazing" air
tightness, heat recovery ventilation.
In the 1990s, in Germany a series of energy-efficient buildings were built,
beginning with the building "Kranichstein" from Darmstadt as a result of the
concept of "passive house" issued by W. Feist and Bo Adamson. Passivhaus
Institut, founded in 1992 by W. Feist has three basic requirements for the
certification of a passive house: Space Heat Demand (or, Heating Load) ≤ 15
kWh/m2/y (≤ 10 W/m2), Pressure Test n50 ≤0.6 h-1, and Primary Energy Demand
(for all energy services)≤120 kWh/m2/y [1]. In addition to the basic requirements,
some other rules of design are established, including: Average ventilation volume
flow with ACH = 0.30 h-1 at least, indoor design temperature of 20 0C, Heat
recovery efficiency of at least 75%, use of the Ground-sourced Heat Exchanger,
demand for Domestic Hot Water (DHW) to be partially or fully covered by solar
collectors [1].
There is a point up to which intense thermal insulation ensures the
maximum efficiency of the investment, which, if exceeded, leads to over-
investment. In this situation one can calculate whether adding additional electrical
panels to the passive house can be a more effective investment than over-insulation
beyond the optimal point [2].
In 1992, Fraunhofer Institute of Solar Energy Systems (Germany)
completed an "autosufficient house ', a building Off-Grid which produces the entire
electricity it needs by means of PV panels [3]. In 1994 Rolph Disch built in Freiburg
(Germany) the building "Heliotrope" with PV panels capable of producing 4-6
times more energy than necessary; this was among the first "Plus-Energy" buildings
[4]. This new opportunity of increasing the energy efficiency as well as the
economic efficiency of the investment by adding PV panels and by making the
bidirectional connection to the electric network led to the need to develop the
concepts of Plus Energy Building and Net-Zero Energy Building [5, 6].
These types of buildings are taken in consideration in the study of this paper.
In one year a Net-Zero Energy Building produces the same same amount of energy
it consumes [7], while a Plus-Energy House produces more energy than it
consumes, thus offering the opportunity to earn an income. Throughout the year
for these buildings there is a monthly balance network monitored by a Net-Metering
System and the factors taken into account are the weighting factors of import-export
of electricity from the exchanges with the network [8, 9]. The surplus energy
exported to the grid is paid by the network operator [10, 11, 12].
Starting from the targets imposed by international organizations and
international treaties that promote environmental sustainability, the development of
the residential sector is considering the use of renewable resources and the reduction
of emissions of greenhouse gases. Thus, mention must be made of the Kyoto
Protocol which obliged the signatory industrialized countries to reduce the
emissions of greenhouse gases by 5.2% in 2010 as compared to the year of 1990
[13]; for the period 2013-2020 the protocol of Doha (2012) is agreed upon, to be
fully adopted in 2015 [14].
In Europe, buildings consume 40% of the total primary energy and they emit
40% of all CO2 emissions [15]. This percentage is high and there are technical and
legal resources to be significantly reduced. An EU directive issued in 2006 and
approved in 2007 considered the following three goals: for the period 2006-2020 to
reduce the primary energy consumption by 20%, renewables to reach a percentage
of 20% and also for the period 1990-2020 CO2 to be reduced by 20% [16]. The
widespread application of the Passive House concept will significantly contribute
to the achievement of the objectives set at the European level. The European
Climate Change Programme (ECCCP 2006) [17] identified the objectives and
strategies for cost effective solutions, standards and energy efficiency measures for
buildings. At the institutional level several incentives are given to investors in clean
energy, including mechanisms that partially or totally cover the investment by non-
reimbursable funds, green cards that over-pay the unit of clean energy produced,
connection to public facilities, etc. Programs funded with support for energy
efficient buildings catalyze the implementation of the European objectives [18].
The European Union Directive on the energy performance of buildings EPBD2010
[19] insists on increasing energy efficiency, by implementing passive heating and
cooling systems and it uses the term "Nearly-Zero Energy" [20, 21] for buildings
that use renewable energy sources in a significant proportion. There are also
requirements to achieve an optimum balance between investment cost and energy
cost savings,a balance should lead to a reduction of the cost over the estimated
economic life cycle, an aspect fully treated in the Supplementing Directive No
244/2012 [22,23,24]. The use of alternative energy is indicated as a way of bringing
the building’s performance at an optimal cost level. Kurnitski et al. [25] and Hamdy
et al. [26] exposed several calculation methodologies for buildings based on
solutions of optimal cost.
Among the requirements of a passive house, three aspects are of interest in
this study and they are related to criteria of cost and energy efficiency: thermal
insulation, renewable energy equipment and energy cost throughout the building's
life cycle. The investment in a project such as a passive house does not mean only
meeting a quality standard, but also meeting the criteria of sustainability (low
energy and as well as energy from renewable resources, cost efficiency, concern
for the impact on the community, environmentally friendly, beneficial ecological
status, and even the use of recycled construction materials). The assessment of a
house only by means of the quality-cost concept is not the most relevant because it
is reduced only to the present time evaluation. The concept of cost throughout the
life cycle of the building brings major contributions to the evaluation of a project
by considering the present cost, the duration of use, the cost of operation, the
interest rate, the escalation of the energy market price, the escalation of price for
various systems and the inflation, in order to update the value of the building. Thus,
it is necessary to underline the advantages of investing in an energy efficient house
involving the cost over a period of the life cycle. The analysis of the life cycle cost
(LCC) is particularly suitable for the assessment of building design alternatives that
satisfy a required level of performance and can be applied to any capital investment
decision where higher initial costs are balanced by future lower operating costs. The
best technical efficiency leads to cost efficiency in operation when the criterion is
energy, but in most cases a further acquisition cost is added and this makes the
analysis based on life cycle methods necessary.
In the studies carried out in the Polytechnic University of Bucharest a
software CYCO-PH in VBA Code has been designed; based on the results of the
balances from PHPP software (delivered by Passivhaus Institut), CYCO-PH is able
to generate an analysis of the life-cycle cost, to make sensitivity analyses for the
main results and to allow risk analyses for alternative projects. It is able to calculate
the heat transfer through envelope based on the outdoor and indoor conditions such
that makes possible sensitivity analysis. In portions of the alghoritms where are
involved the equipments of the house, in its input are used directly the normalized
values of the powers (thermal, electric) obtained from the output of PHPP where
are applied the rigours of Passive House Institute from Darmstadt. Practically, it
comes with an analysis that PHPP does not covers in the domain of economics and
welcomes the European directives that aim to position the buildings in cost-optimal
zones. Climatic data contain monthly normalized values of the temperature and
solar radiation, particularly it was necessary to split the year in two seasons (cold
and warm) and establish the average values for both in order to apply in the
calculation the criterion that in winter to be assured 20 0C and in summer 25 0C (for
at least 90% of the time).
It is necessary to display information about the economic environment as the
latter explains the information about the real conditions of the operation of an
investment. A report by GTM Research for the period 2012-2017 provides a
reduction of 38.8% of the prices of PV panels from 0.5 $/W (0.36 Euro/W) to 0.36
$/W (0.26 Euro/$) [27], a similar trend everywhere, which means an average
reduction of about 17.2% (a negative rate of escalation) from one year to another
for the respective period. If throughout the next 25 years prices varied with a
constant escalation rate of 17.2% that would mean a price of 0.003 $/W at the end
of the period; this value is too low and unsustainable. A more realistic forecast is to
consider that in the next 25 years the price of PV panels will halve from 0.50 $/W
to 0.25 $/W, which means a real average rate of escalation of the price of 0.027
(2.7%) from one year to another. Beyond specific prices $/W or Euro/W what is
important are the trends in time that appear to be about the same for all countries.
The escalation of electricity prices influences significantly the balance of the
costs of an energy-efficient house and this is how the price escalation based on
Eurostat statistics for the period 2007-2012 is considered (an average increase of
0.85% year on year [28]). In this paper are considered prices of fossil fuels (natural
gas) of 0.28 Euro/kWh and also the price for heat from the District Distribution of
0.40 Euro/kWh. The forecast of the rate of energy escalation applies to all types of
energy from industry (a simplification that includes solid fuel, gas fuel, electricity
or mix of energy) and is 0.007 (0.7%) from one year to another for long term periods
(more than 25 years).
Eurostat [29] provides statistics about commercial interest rates (retail interest
rate) which, for the period 2001-2011, was between 0.81% - 4.63% with a multi-
annual average of 2.69%. However, in general, formal values of 3.0-4.0% are
considered, and the most often used value (or required by official procedures) is
3.0%.
Eurostat [30] shows an inflation of 2% in the last 20 years in Europe (in 2013
the inflation was of 1.6%) with a slightly descending trend and the value of 1.5% is
considered the best estimate of the inflation for the next 30 years. In this study are
very important the escalation of the energy price and of PV panels price, which are
strongly related to issues of economic efficiency of the investment; these variables
are kept as such for further use.
2. Literature reviews
There are a number of works in which the method of life cycle cost of
buildings is used. Fuller in [31, 32] provides a set of methodologies for the life cycle
cost analysis (LCCA) of the buildings. Głuch and Baumann (2004) [33] made a
conceptual presentation of the method of LCC and mentioned the support that it
provides for the investment decision and the environmental decision. They insisted
on the essential difference between LCC method and the Life Cycle Assessment
(LCA) method. Among the methods complementary to the life cycle cost analysis
of buildings mention must be made of the method of "life-cycle energy" (LCE)
approached by Cole and Kernan (1996) [34] Sartori and Hestnes (2007) [35]
Huberman and Pearlmutter (2008) [36] Ramesh et al. (2010) [37], where the notion
of energy for traversing and issuing balances of every stage of life of the building
is essential. Feist (1997) [38] also describes the evolution of cumulative primary
energy for various solutions of energy efficient houses, related to a typical standard
house in the 1980s. IEEA [39] gave a comparison of the extra capital cost and of
the cost of passive houses in different countries and in some cases they are very
different from case to case with values even higher than 50%. This suggests the
need for a dedicated analysis for every project, statistics are informative and in
order to interpret them correctly one needs to take into account specific pricing from
country to country and even from region to region. Badescu (2007) [40] studied a
series of alternative heating solutions and he found that for time periods which are
longer than 20 years the GHP solution tends to be the most efficient from an
economic point of view. Audenard et al. (2008) [41] conducted an economic
analysis of a passive house, comparing it with a low energy house and with a
standard house. In that case, if energy cost remains constant the passive house
equals the cost of a standard house in about 29 years and when the cost of electricity
would be with an escalation rate of 5% then the cost equalization period is reduced
to 18 years. Versele et al. (2009) [42] considered the life cycle cost and the payback
period analysis of a retrofitted house in Belgium and he divided the problem into 4
scenarios of fulfillment standard requirements for houses among which the passive
house requirement was included. He found that the additional investment to achieve
a passive house standard was 27% higher than the cost scenario for a standard
house. In a study for a Net-Zero Energy House with a solar combisystem, Leckner
and Zmeureanu (2011) [43] found that the low price of electricity in Montreal made
the full return of the investment in solar technology impossible to be achieved.
Marszal and Heiselberg (2010) [44] made an analysis of the life cycle cost of a
multi-floor building Net-Zero Energy for a period of 30 years and found that
investing in a heat pump is more advantageous than using the district heating grid.
3. Method
A general model of the life cycle cost includes a number of factors of
varying economic conditions (variability of bank interest rates, inflation, price
escalation); every cost is considered updated at the present value:
𝐿𝐶𝐶 = 𝑃𝑉 = 𝑃𝑉𝐼𝑛𝑣𝑒𝑠𝑡 − 𝑃𝑉𝑁𝑜𝑛𝑅𝑒𝑖𝑚𝑏 + 𝑃𝑉𝐸𝑛𝑒𝑟𝑔𝑦 − 𝑃𝑉𝑆𝑢𝑏𝑠𝑖𝑑 + 𝑃𝑉𝑅𝑒𝑝𝑙 + 𝑃𝑉𝑂𝑀&𝑅
+𝑃𝑉𝑃𝑒𝑟𝑠 + 𝑃𝑉𝑇𝑎𝑥𝑒𝑠 + 𝑃𝑉𝐸𝑛𝑣𝑖𝑟 − 𝑃𝑉𝑅𝑒𝑠𝑖𝑑 + 𝑃𝑉𝐷𝑒𝑐𝑜𝑚𝑚 (1)
A reduced form of the equation (1) of LCC is found in [31,32]. Aspects of
utilities, staff, tax, residual value, decommissioning are not taken into account in
this analysis, as they are not relevant to the purpose of the study. At the same time,
they tend to have the same values throughout the change of the design of the houses
involved. To highlight the issue of economic efficiency of the building, the
following components will be considered arbitrary in equation (2):
𝐿𝐶𝐶 = 𝑃𝑉𝐼𝑛𝑣𝑒𝑠𝑡 + 𝑃𝑉𝐸𝑛𝑒𝑟𝑔𝑦 − 𝑃𝑉𝑆𝑢𝑏𝑠𝑖𝑑 + 𝑃𝑉𝑅𝑒𝑝𝑙 + 𝑃𝑉𝑂𝑀&𝑅
= (𝑃𝑉𝑆𝑡𝑟𝑢𝑐𝑡 + 𝑃𝑉𝐼𝑛𝑠 + 𝑃𝑉𝐸𝑞𝑢𝑖𝑝) + 𝑃𝑉𝐸𝑛𝑒𝑟𝑔𝑦 − 𝑃𝑉𝑆𝑢𝑏𝑠𝑖𝑑 + 𝑃𝑉𝑅𝑒𝑝𝑙 + 𝑃𝑉𝑂𝑀&𝑅
(2)
Simplifications are made by ignoring the costs involving fixed funds such as
national or international grants (we considered only subsidies for the production
process), taxes, environmental taxes, residual value, the cost of decommissioning
at the end of life cycle. This is done in order to explore the key factors of economic
interaction throughout the economic life cycle of a house.
PV panels are considered extensively with a life cycle of 25 years, OM&R
costs (operation, maintenance and repair) are considered annually as 0.1% of the
entire investment. There are considered in calculation government subsidies in
Green Certificates (4 Green Certificates=4x0.027 Euro/kWh=0.108 Euro/kWh)
which are given for the first 15 years of operation and production, thereby
improving cash flow and reducing the period of payback.
Further on, for the calculation we considered the inflation rate ri, the real
rate of escalation (of energy or equipments such as PV panels) rre and the discount
rate in order to convert the future values FV into present values PV by an overall
actualization rate ra:
𝑃𝑉 = 𝐹𝑉1
(1+𝑟𝑎)𝑛= 𝐹𝑉
(1+𝑟𝑖)𝑛(1+𝑟𝑟𝑒)𝑛
(1+𝑟𝑟𝑑)𝑛= 𝐹𝑉
(1+𝑟𝑖)𝑛(1+𝑟𝑛𝑒)𝑛
(1+𝑟𝑛𝑑)𝑛 (3)
where n is the n-th year in the evaluation, and the overall actualization rate ra is:
𝑟𝑎 =(1+𝑟𝑟𝑑)
(1+𝑟𝑖)(1+𝑟𝑟𝑒)− 1 (4)
This approach includes all three terms (discount rate, inflation rate and
escalation rate) with their proper variation generalizing the two approaches
"constant dollars/ currency" (which uses real rates) and "current dollars/currency"
(which uses nominal rates).
In this study the rate of inflation is not considered. In order to get more
relevant results from a technical point of view we will keep constant the purely
economic conditions related to inflation because they are more appropriate for the
analyses which insist on aspects of the financial market.
The fact that money is the common element of all goods gives us the
opportunity to analyze heterogeneous solutions and their combinations. The
analysis of the economic efficiency may use one or more of the criteria in Table 1.
Economic efficiency is met for the situations of the minimum Life-Cycle
Cost (LCC), maximum Net Saving (NS), maximum Saving-to-Investment Ratio
(SIR), maximum Adjusted Internal Rate of Return (AIRR) and minimum
Discounted Pay-Back Time (DPBT). Thus, we obtained the necessary information
on whether the additional value of the investment is eligible or not.
Table 1 Specific variables of evaluation of the economic efficiency of a project Variable Expression Required
LCC
∑ ∑ 𝑃𝑉𝑖𝑗
𝑁
𝑖=0
𝑀
𝑗=1
= ∑ ∑𝐹𝑉𝑗𝑖
(1 + 𝑟𝑎,𝑗)𝑖
𝑁
𝑖=0
𝑀
𝑗=1
= 𝐼0 + ∑ ∑𝐹𝑉𝑗𝑖
(1 + 𝑟𝑎,𝑗)𝑖
𝑁
𝑖=1
𝑀
𝑗=1
(5) Minimal
NS 𝐿𝐶𝐶𝐵𝑎𝑠𝑒 𝐶𝑎𝑠𝑒 − 𝐿𝐶𝐶𝐴𝑙𝑡𝑒𝑟𝑛𝑎𝑡𝑖𝑣𝑒 = −∆𝐼0 − ∑ ∑∆𝐼𝑗𝑖
(1 + 𝑟𝑎,𝑗)𝑖
𝑁
𝑖=1
𝑀
𝑗=1
+ ∑ ∑𝑆𝑗𝑖
(1 + 𝑟𝑎,𝑗)𝑖
𝑁
𝑖=1
𝑀
𝑗=1
(6) >0, Maximal
SIR ∑ ∑ 𝑆𝑗𝑖/(1 + 𝑟𝑎,𝑗)
𝑖𝑁𝑖=1
𝑀𝑗=1
−∆𝐼0 − ∑ ∑ ∆𝐼𝑗𝑖/(1 + 𝑟𝑎,𝑗)𝑖𝑁
𝑖=1𝑀𝑗=1
(7) >1,
Maximal
AIRR (1 + 𝑟𝑟)𝑆𝐼𝑅1/𝑁 − 1 (8) >rd, Maximal
DPBT ≈ 𝐼𝑁𝑇 {𝑅𝑂𝑂𝑇 [𝑖, −∆𝐼0 − ∑ ∑∆𝐼𝑗𝑖
(1 + 𝑟𝑎,𝑗)𝑖
𝑁
𝑖=1
𝑀
𝑗=1
+ ∑ ∑𝑆𝑗𝑖
(1 + 𝑟𝑎,𝑗)𝑖
𝑁
𝑖=1
𝑀
𝑗=1
= 0]} (9) <LC,
Minimal
where i=0...N is the year number, j=1...M is the component of the investment, I0 is the initial investment, ΔI0 is the difference of investment of the alterntive project related to the base case, Sji is the saving from the component j in year i in operational
costs of the alternative project related to base case, ΔIji is the additional investment from the component j in year i of the
alternative project related to base case.
After the payback at the end of Discounted Pay Back Time or at the end of
life-cycle there is a period when the investor has a remanent value.
In order to quantify the increase of the energy efficiency by reducing the
energy consumption or by the production of electricity (which can be economically
exploited by the bi-directional electric energy exchange with the public grid through
a metering system and by starting a commercial relationship with the District [10,
11, 12]), a period of operation of the house for 30 years is predefined. This is
necessary in order to close the time loop algorithm for the system performance
evaluation by considering a life cycle which in this case is the usual period of 30
years and in some results periods of up to 60 years will be included.
Two approaches are basic in the evaluation of economic systems: the
simplest economic conditions, where all variations are neglected in the economic
environment (inflation, bank interest rates, escalating prices) as a most conservative
approach; economic conditions considered the most probable based on the existing
information (from published statistics), and they imply "the most likely" specific
values of the economic environment derived from a forecasting analysis. This paper
uses both hypothesis of economic conditions in order to present the things in a rough
view (by considering simplest economic conditions) and also in a more balanced
evaluation (by considering the best forecasted economic conditions for the future
period of evaluation). As result, it is obtained a complete picture of the way the
project could follow.
The techniques for analyzing the variable economic environment involve
deterministic approaches (which are used in this study) considering in analysis the
variation of one or of combinations of variables around the predicted point. Another
technique is the probabilistic one where a probability factor is added to every value
considered; however, in order to proceed to such an analysis it is necessary to
process and correlate large amounts of statistical data.
4. Technical data of the Passive House “POLITEHNICA”
The building “POLITEHNICA” is built at University POLITEHNICA of
Bucharest at the follwing coordinates: 44.4380N Latitude, 26.0470E Longitude and
76.6 m Altitude. It contains two houses: the “East House” and the “West House”
that are placed in a common external envelope. Table 2 shows the geometric
parameters of the houses and of the building as a whole, highlighting its high
compactness which characterizes a great spaciousness at a minimal external surface
with the overall effect of reducing the heat losses.
Table. 2 Geometry information of the Passive House [46] Geometric Indicator Indicator value for each case
“East House” “West House” Overall
Treated floor area [m2] 140 140 280
Envelope area [m2] 481.6 481.6 797.2
Indoor air volume [m3] 435.3 435.3 870.6
Compactness C=V/S [m3/m2] 1.628 1.628 1.967
Table 3 gives information about the envelope of the building and about the thermal
properties of its parts.
Table. 3 Envelope information of the Passive House [46]
Envelope Component Geometric
indicator
Thermal
indicator
thk [mm] Stotal [m2]
Uvalue [W/m2/K]
Walls
Vertical
wall
Bricklayer 250 188.8 0.122
Thermal insulation layer 300
Roof
Roof Concrete Layer 130
188.8 0.107 Roof Thermal Insulation Layer 120
Roof Thermal Insulation Layer 120
Floor Floor Thermal Insulation Layer 150
188.8
Floor Concrete Layer 120 0.105
Windows
3x Glass layers+2x Argon 90% layers 44 64.04
0.800 Frame 86
Doors 70 3.78 0.800
The Passive House characteristics have been processed through certified
PHPP software (Passivhaus Planning Package) of the Passivhaus Institute from
Darmstadt (Table 4). On the south-facing roof angled at 15 degrees are mounted 26
PV panels (PVx1) that generate the specific space energy of 37.5 kWh/(m2y); also
are mounted 2 solar collectors with the power of 2.5 kW each.
Table. 4 Certification parameters of the Passive House Indicator Indicator value for each case
Required East House West House Overall
Specific Space Heat Demand, [kWh/m2/y] 13 13 12.5 ≤15
Specific Space DHW Demand, [kWh/m2/y] 18 18 18 -
Specific Space Electric Energy Consum., [kWh/m2/y] 45.8 30.5 38.1 -
Total Specific Primary Energy Demand, [kWh/m2/y] 119 79 99 ≤120
The “East House” has an Earth-to-Air Heat Exchanger (EAHX) (Fig. 1a)
with a maximum ventilation rate of 0.5 h-1. The "West House" has a geothermal
heat pump (GHP) (Fig. 2b) with the thermal load of 5.4 kW and it is based on a
drilling of 80 m depth [46, 47].
An evaluation of the balance between the electric energy production and the
electric energy consumption results in approximately equal values and suggests that
the Passive House “POLITEHNICA” is a Net-Zero Energy Building (Net-ZEB).
The parameters are based on the evaluation of PHPP and at present measurements
are being taken throughout an entire year in order to obtain real data. Stutterecker
pointed out that it is important whether the definition is based only on design data
or also on valid monitoring data [11].
Fig. 1 Thermal instalations of the “POLITEHNICA” building: a) “East House”, b) “West House”
[46, 47, 48] a)
1 – Solar Collector, 2 – Cold Water Inlet, 3 – Hot Water
Tank, 4 – Domestic Hot Water Outlet, 5 Electric Resistance
Heater, 6 – Heat Recovery Unit (HRU), 7 – Water-Air Heat Exchanger, 8 – Pumps Station, 9 – Geothermal HEat
Exchanger, 10 – Passive Cooling Heat Exchanger, 11 –
Hydronic Radiant Panel
b) 1 – Solar Collector, 2 – Cold Water Inlet, 3 – Hot Water
Tank, 4 – Domestic Hot Water Outlet, 5 Electric
Resistance Heater, 6 – Heat Recovery Unit (HRU), 7 – EAHX By-Pass, 8 – Condensate Drain Well, 9 – Earth
To Air Heat Exchanger (EAHX), 10 – Electric Radiant
Panel
Heat Recovery Units (HRU) of the system of ventilation have an efficiency
of 90%. The efficiency of the equipments corelated with factors of utilization are
translated in heat gains that are processed by PHPP software.
The ocupancy is considered as per the one indicated by Passive House
Institut, 1 person/35 m2 [1] . Temperature setpoint of the indoor air is 20 0 C in the
winter and 25 0 C in the summer for a balanced evaluation while the design
temperature is 20 0 C.
In [49], Feist has provided some valuable rules of efficient design of the
buildings such as passive houses and he has also built an argument accompanied by
an energy diagram for the limit case when the dedicated heating system of the
building would be removed, still keeping a minimum level of thermal comfort. He
believes that by applying the principles of "superglazing" and "superinsulation" a
quantity of heat required for heating of the house still exists but its level is so low
that it can be neglected at the limit. Fig. 2 [50] shows the costs diagram (for a life
cycle of 30 years) based on information from the passive house POLITEHNICA
mainly related to the thermal insulation thickness and has an analogy with the
diagram presented by Feist in [49].
Fig. 2 Diagram of specific space cost considering removing the dedicated heating systems when
the passive house standard is met [50]
5. Model of analysis
The interest is to find the economic benefits of a passive house with all the
technical variations over a life cycle, relative to the base case of a standard building.
The choice of a particular investment project among its alternatives should be
explained on the basis of economic criteria.
The economic information of the passive house POLITEHNICA allowed
the reproducing of its economic behavior at theoretical level, and further,
investigation was made extending to other alternatives derived from its basic core.
We explored the variation of equipping the house ( generating H13-H25)
while the same thermal insulation is maintained (300 mm as in the design case of
the passive house "Politehnica"), the same air tightness. The applied
abstractizations and limitations facilitate to determine the differences by economic
performance criteria. The house is compared with the standard insulation house
H12 which is also derived from the design of the house POLITEHNICA but has a
thermal insulation thickness of 100 mm.
All variables that are used are expressed in specific space energy and
specific space heat calculated for a year in terms of primary energy. If one wants to
express variables in secondary energy (electricity), then the following
transformation can be used:
𝑓𝑃−𝑆 =𝐸𝑝
𝐸𝑆=
𝑄𝑝
𝑄𝑆= 2.6 𝑘𝑊ℎ/𝑘𝑊ℎ (10)
The values of thermal loads for the passive house POLITEHNICA are
evaluated by the PHPP software required by the Passivhaus Institut for certification.
Balance of heating in the cold season:
𝑄𝐻 = (𝑄𝑤𝑎𝑙𝑙𝑠 + 𝑄𝑓𝑒𝑛 − 𝑄𝑠𝑜𝑙𝑎𝑟 + 𝑄𝑔𝑟𝑜𝑢𝑛𝑑 − 𝑄𝑖𝑛𝑡 − 𝑄𝑣𝑒𝑛𝑡&𝑙𝑒𝑎𝑘) (11)
Balance of cooling in the warm season:
𝑄𝐶 = (−𝑄𝑤𝑎𝑙𝑙𝑠 − 𝑄𝑓𝑒𝑛 − 𝑄𝑠𝑜𝑙𝑎𝑟 − 𝑄𝑔𝑟𝑜𝑢𝑛𝑑 − 𝑄𝑖𝑛𝑡 + 𝑄𝑣𝑒𝑛𝑡&𝑙𝑒𝑎𝑘) (12)
Table 5 provides information about the thermal loads extracted from PHPP
in order to be used in the equations of thermal balance of the passive house and its
derivatives. Those loads are design values with a degree of redundance that it is
able to cover partial loads derived from the variation of the weather, situational
consumptions, overlaping of the processes, etc.
Table. 5. Thermal loads of the Passive House POLITEHNICA “East” House “West House
Thermal Load Cold Season Warm Season Cold Season Warm Season
QH [kWh/m2/y] 12 - 13 -
QC [kWh/m2/y] 8.1 - 7.9
QDHW [kWh/m2/y] 18 18
Qwalls [kWh/m2/y] 17.8 11 17.8 11
Qfen [kWh/m2/y] 13.4 8.6 13.4 8.6
Qsolar [kWh/m2/y] 19.3 19.3 18.1 18.1
Qvent&leak [kWh/m2/y] 7.7 40.4 7.5 39.1
Qint [kWh/m2/y] 10.3 10.3 10.3 10.3
Qground [kWh/m2/y] 2.7 1 2.7 1
The information on thermal loads can also be obtained by processing models
in platforms such as TRNSYS, EnergyPlus, Simulink that can further perform
balances of them. In this study a VBA programming code was created in order to
achieve a conservative balance of the thermal loads (supplied by PHPP) by using
conditional, Boolean logic functions and threshold functions.
The equations that certify the passive house as per Passive House Institute
criteria [1] and also verify the thermal/electrical loads are presented below:
𝑄𝐻 , 𝑄𝐶 ≤ 𝑄𝑃𝐻𝐼 = 15 𝑘𝑊ℎ/𝑚2/𝑦 (13)
𝐸 = 𝑄𝐻 + 𝑄𝐶 + 𝑄𝐷𝐻𝑊 + 𝐸𝐸𝑙 ≤ 𝐸𝑃𝐻𝐼 = 120 𝑘𝑊ℎ/𝑚2/𝑦 (14)
where (13) checks the heating/cooling load and (14) the total primary energy
consumed in the house.
Balance equations of heating and hot water storage of the “East House”:
𝐸𝑃𝑉_𝐻𝑉𝐴𝐶1 + [𝑄𝐸𝐴𝐻𝑋 − 𝑄𝐻1 − 𝑄𝐶1]− = 0 (15)
𝐸𝑃𝑉_𝑆𝑡𝑜𝑟𝑎𝑔𝑒1 + [𝑄𝑆𝐶1 − 𝑄𝐷𝐻𝑊1]− = 0 (16)
where [ ] _ extracts the negative value of the expression, and when the expression
is positive then the result is null. This operator is used to describe the electric power
supply that comes in only when the thermal systems of renewable energy are over-
loaded by the thermal load requirements.
The electricity needed for the house with an EAHX system is:
𝐸𝑁1 = 𝐸𝑃𝑉_𝐻𝑉𝐴𝐶1 + 𝐸𝑃𝑉_𝑆𝑡𝑜𝑟𝑎𝑔𝑒1 + 𝐸𝑃𝑉_𝐸𝑙1 = −[𝑄𝐸𝐴𝐻𝑋 − 𝑄𝐻1 − 𝑄𝐶1]− − [𝑄𝑆𝐶1 − 𝑄𝐷𝐻𝑊1]− + 𝐸𝑃𝑉_𝐸𝑙1
(17)
Balance equations of the heating and the hot water storage of the “West House”:
𝐸𝑃𝑉_𝑆𝑡𝑜𝑟𝑎𝑔𝑒2 + [𝑄𝐺𝐻𝑃 + 𝑄𝑆𝐶2 − 𝑄𝐻2 − 𝑄𝐶2 − 𝑄𝐷𝐻𝑊2]− = 0 (18)
The electricity needed for the house with GHP system is:
𝐸𝑁2 = 𝐸𝑃𝑉_𝑆𝑡𝑜𝑟𝑎𝑔𝑒2 + 𝐸𝑃𝑉_𝐸𝑙2 = −[𝑄𝐺𝐻𝑃 + 𝑄𝑆𝐶2 − 𝑄𝐻2 − 𝑄𝐶2 − 𝑄𝐷𝐻𝑊2]−
+ 𝐸𝑃𝑉_𝐸𝑙2
(19)
Situational peak loads can give an influence on the balances, but for this
study that is pursuing only an economic and global evaluation of the energy status
of the building the conservative balances (that use averaged values along of a year)
give good results.
The total required (necessary) energy is:
𝐸𝑁 = {
𝐸𝑁1 + 𝐸𝑁2, if the building solution is 𝐸𝐴𝐻𝑋 + 𝐺𝐻𝑃2𝐸𝑁1, if the building solution is 𝐸𝐴𝐻𝑋𝑥2 2𝐸𝑁2, if the building solution is 𝐺𝐻𝑃𝑥2
(20)
For a Plus-Energy house the following relation occurs:
𝐸𝑃𝑉 − 𝑓𝑔𝑟𝑖𝑑 ∙𝐸𝑁
𝑓𝑃−𝑆= 𝐸𝑔𝑟𝑖𝑑_𝑏𝑎𝑙𝑎𝑛𝑐𝑒 (21)
where fgrid ≈ 1.01 is an index of the energy interaction building- network [7]
monitored through a metering system. The following criteria may be established:
𝐸𝑔𝑟𝑖𝑑_𝑏𝑎𝑙𝑎𝑛𝑐𝑒: {< 0, for Traditional, Standard or Nearly-ZEB Building≈ 0, for Net-ZEB > 0, for Plus-EB
(22)
The amount of money paid to or resulting from the export of energy will be
𝐶𝑒(𝑖) = 𝑐𝑒 ∙ 𝑖 ∙ 𝐸𝑔𝑟𝑖𝑑_𝑏𝑎𝑙𝑎𝑛𝑐𝑒 (23)
where ce [Euro/kWh] is the cost per unit of energy, and i is the i-th year of the start
of operation. This case is available by not considering actualization rates (simple
and constant economic conditions).
A house is a set containing heterogeneous elements. In order to carry out
the analysis we proceeded to a theoretical decomposition of the passive house in its
parts, thus providing a diversification of the options (something like puzzle pieces)
with a level of granularity and scalability. The main components of the passive
house considered in the model are the concrete structure (walls, foundation, etc.),
the thermal insulation, the glazing, the renewable energy systems (or
conventional/classical HVAC systems), the heat recovery system, a solar collector
system with a DHW storage tank, and the photovoltaic PV panels system.
Scalability is especially related to some specific variation of a component -
for example, in the study [50] after the thermal insulation was extracted as a part
from the assemble of the passive house, a variation of the thickness was performed
for a comparative study. The granularity of the variation is related to the magnitude
of the steps of variation. In this study scalability is mainly related to the variation
of the solution of the renewable energy system (EAHX + GHP, EAHXx2, GHPx2)
and of the number of PV panels. This treatment of a heterogeneous system finds the
solution due to the fact that the common denominator of all components is money.
Accepting an additional cost for a building only for its properties of super-
insulation is not enough. A passive house involves greater complexity than super-
insulation, it also includes renewable energy equipment such as EAHX or GHP,
solar collectors, solar photovoltaic panels, etc. which add extra cost to the
investment.
Table 6 shows the details of the design solutions for a range of houses (H12-
H25) with their facilities of renewable energy equipments. The solution H19 of the
passive house "POLITEHNICA" is "highlighted" and it has EAHX in the "East
House" and GHP in the "West House", two solar collectors (SC), and a photovoltaic
system of 26 PV panels (PV panels PVx1 = 26 ↔ 37.5 kWh/m2/y).
Table 6 Classification of the houses energy efficiency by adding equipments of renewable energy
House
Ins.
thick.
of the
walls
[mm]
Glazing
Classic
Heating
system/
Cooling
System
Solar Coll.
/PV Panels
Equipent of
Ground
Sourced Energy
Heating Load/
Cooling Load
[kWh/m2/y]
Energy Classification
Treshold value/ Description
[kWh/m2/y]
H12 100 2 Pane yes/yes No/No No 58.2/34.9 ≤65, Standard Energy
H13 300 3 Pane yes/yes No/No No 13.5/8.0 ≤15, Super-Insulated Bld.
H14 300 3 Pane No/No SCx2/PVx1 EAHXx2 13.5/8.1 ≤15, Passive,Nearly-ZEB
H15 300 3 Pane No/No SCx2/PVx1 GHPx2 13.5/7.9 ≤15, Passive,Nearly-ZEB
H16 300 3 Pane No/No SCx2/PVx1 EAHX+GHP 13.5/8.0 ≤15, Passive,Nearly-ZEB
H17 300 3 Pane No/No SCx2/PVx1 EAHXx2 13.5/8.1 ≤15, Passive, Net-ZEB
H18 300 3 Pane No/No SCx2/PVx1 GHPx2 13.5/7.9 ≤15, Passive, Net-ZEB
H19 300 3 Pane No/No SCx2/PVx1 EAHX+GHP 13.5/8.0 ≤15, Passive, Net-ZEB
H20 300 3 Pane No/No SCx2/PVx2 EAHXx2 13.5/8.1 ≤15, Passive, Plus-EB
H21 300 3 Pane No/No SCx2/PVx2 GHPx2 13.5/7.9 ≤15, Passive, Plus-EB
H22 300 3 Pane No/No SCx2/PVx2 EAHX+GHP 13.5/8.0 ≤15, Passive, Plus-EB
H23 300 3 Pane No/No SCx2/PVx5 EAHX+GHP 13.5/8.1 ≤15, Passive, Plus-EB
H24 300 3 Pane No/No SCx2/PVx5 EAHXx2 13.5/7.9 ≤15, Passive, Plus-EB
H25 300 3 Pane No/No SCx2/PVx5 GHPx2 13.5/8.0 ≤15, Passive, Plus-EB
The information shown in Table 6 calls for explanations on the energy
classification of houses solutions in order to give a synthetic picture of the status of
each. Thus, the following terms are used: "Super-insulated building", a house with
a corresponding level of insulation comparable to a passive house (as understood
by the Passivhaus Institut) with a conventional/classical heating system; Nearly-
Zero Energy Building (Nearly-ZEB) which is a building in accordance with the
requirements of the EPBD 2010/31/EU [19] and which also meets all the
requirements of the Passivhaus Institut from Darmstadt; Net-Zero Energy Building
(ZEB-Net) which is an on-grid building capable of producing as much energy as
it consumes throughout one year ; Plus-Energy Building (Plus-EB) which is an on-
grid building capable of producing more energy than it consumes thoughout one
year.
6. Results
Fig. 3 shows the diagram involving the cost investment in solutions H12-
H25 by adding different combinations of renewable energy systems including PV
panels at different power envelopes (1x, 2x and 4x relative to the solution of the
minimum number of panels 1x = 26 PV panels which basically obtained the status
of net-zero energy for "POLITEHNICA" house).
Fig. 3 Specific Space Cost of investment in different solutions of houses H12 to H25
H12 is the standard building and the simplest solution with a thermal
insulation thickness of 100 mm, and the other solutions (with insulation thickness
of 300 mm) meet the passive house standard (and Nearly-ZEB principles), and Plus
Net ZEB-EB. The latter have specific costs associated with their systems (Fig. 3).
If the building is based solely on a geothermal heat pump solution (GHPx2),
then the cost is particularly high especially because these systems are generally
more suitable for large buildings. The EAHXx2 alternative is the cheapest in terms
of initial investment, followed by the combined solution EAHX + GHP. However,
in the design execution of the passive house "Politehnica" the combination of two
different solutions was preferred, a heterogeneous approach which does not provide
the most effective combination but which is chosen on the grounds of challenges of
the research and of diversified teaching.
The starting point is the initial investment and the end point of the economic
cycle is usually reached after 30 years, but the analysis can be extended to 60 years
or more. Fig. 4 shows the total cost of the houses involving life cycles of 24 years
(even before the end of the operation of PV panels), 30, 40, 50 and 60 years.
a) b)
Fig. 4 Specific Space Life Cycle Cost LCC on time spans of 24, 30, 40, 50, 60 years: a) Life Cycle
Cost in the simplest economic conditions; b) Life Cycle Cost in the best forecasted economic
conditions
The longer the period of the life cycle cost, the more obvious the disadvantage
of the standard house H12. Some more defined results that allow a more direct
analysis solution versus solution are those derived from the "break-even" diagram
of cost equalization.
The "break-even" analysis of cost equalization (fig. 5) is made for the houses
H12-H25 in which H12 is the base case (or the standard reference). Fig. 5b also
shows a reduced list where houses H13, H16, H19, H22 and H25 are considered;
these houses have the same renewable EAHX + GHP system as the passive house
POLITEHNICA (H19) does, in order for us to have a comparative view of the
results. The life cycle cost of standard house H12 is matched by other alternatives
in 16-33 years in the simplest economic conditions (a conservative case) and in 16-
26 years if the best forecasted economic conditions are considered. The "break-
even" analysis of the simplest economic conditions (with the exclusion of the
escalation of prices of energy and PV panels) and in the most probable economic
conditions (average negative escalation of prices of the PV panels of -2.7% per year
and an annual escalation of energy prices of +0.7%) shows the moments when the
energy efficient solutions H13-H25 are able to recover the additional investment
against the standard house H12.
a) b)
c) d)
Fig. 5 Break-even analysis of the cost: a) extended list of houses in the simplest economic
conditions; b) reduced list of houses in the simplest economic conditions; c) extended list of
houses in the best forecasted economic conditions d) reduced list of houses in the best forecasted
economic conditions
The graphs of Cumulative Cash Flow or Net Saving (fig. 6) are related to
the base case H12. They complement the information in Fig. 5 to show the evolution
of the recovered amount over time due to improved efficiency after initially
investing more money.
a) b)
c) d)
Fig. 6 Specific Space Discounted Cash Flow or Net Saving: a) extended list of houses in the
simplest economic conditions; b) reduced list of houses in the simplest economic conditions; c)
extended list of houses in the best forecasted economic conditions d) reduced list of houses in the
best forecasted economic conditions
Table 7 shows the situation when the heating and DHW systems of the
standard house H12 based on the natural gas fuel are replaced. Hypothetical
replacement is made by systems of heating and DHW based on electricity (when
the cost of investment is the same as in the classical case but with a higher operating
cost) or District Distribution (when the investment in facilities for heating and
DHW is almost zero but the operation is cheaper than the classic case of fuel gas)
respectively.
Also are seen major differences in the duration of the recovered amount,
electrical heating system being the easiest to be replaced by the renewable energy
equipment while the option of District Distribution is the most difficult to be
replaced by the alternatives.
Table 7 Discounted Pay-Back Time (DPBT) for different references of heating and DHW systems
in the best forecasted economic conditions
Heating & DHW Systems H13 H14 H15 H16 H17 H18 H19 H20 H21 H22 H23 H24 H25
Gas Fuel System - DPBT [years] 20 16 24 20 18 26 21 16 21 19 16 19 18
Electric System- DPBT [years] 13 9 14 12 11 16 14 12 15 14 13 15 14
District Distribution- DPBT [years] 20 19 27 23 20 28 23 18 27 21 17 26 19
In comparison with the District distribution case, particularly H15, H18, H21,
H24 have a higher DPBT recovery period because the initial investment for the
solutions with GHPx2 is bigger and amplify the delay of the money recovery. At
the same time, the change of the PV panels after 25 years makes the Net Savings
(NS) become negative for a gap of several years, and then they become definitively
positive.
A sensitivity analysis is carried out in order to evaluate the solutions of
houses in hypothetical economic conditions. This analysis takes into account the
life cycle cost, net savings, the savings to investment ratio and the internal rate of
return, the payback time.
If multiple variables of evolution of a system are forecasted, then around the
point of maximum probability the response of the system to the excitation of one
variable is studied when the other variables are maintained constant at their
maximum probability (the average point for normal distributions).
𝐶(𝑥1, … , 𝑥𝑖 , … , 𝑥𝑛) = 𝐶(𝑥1, … , 𝑥𝑖, … , 𝑥𝑛) +𝜕𝐶
𝜕𝑥1𝑑𝑥1 + ⋯ +
𝜕𝐶
𝜕𝑥𝑖𝑑𝑥𝑖 + ⋯ +
𝜕𝐶
𝜕𝑥𝑛𝑑𝑥𝑛
≈ 𝐶(𝑥1, … , 𝑥𝑖, … , 𝑥𝑛) + (𝜕𝐶
𝜕𝑥1)
𝑥1
(𝑥1 − 𝑥1) + … + (𝜕𝐶
𝜕𝑥𝑛)
𝑥𝑛
(𝑥𝑛 − 𝑥𝑛)
(24)
The limits of the variations are established in the equation (25):
𝑚𝑎𝑥, min[𝐶(𝑥1, … , 𝑥𝑖, … , 𝑥𝑛)] = 𝑚𝑎𝑥, min[𝐶(𝑥1, … , 𝑥𝑖 , … , 𝑥𝑛), … , 𝐶(𝑥1, … , 𝑥𝑖, … , 𝑥𝑛)]
(25)
The real escalation rate is modified by the factor of variation fs that comes in order
to do sensitivity analysis:
𝑟𝑟𝑒,𝑠 = (1 + 𝑓𝑠)𝑟𝑟𝑒 (26)
Sensitivity analysis and interaction between the influences of variables
gives the main path of variation of the implied function. The biggest interest in this
kind of analysis is on buildings that imply the combination of the renewable energy
systems EAHX+GHP because they are more correlated with the house
POLITEHNICA. Fig. 7 shows the influences of the rate of escalation of the prices
of PV panels and of the energy around their best forecasted point. H16 does not
have its own production of electricity and LCC increases with the price of energy.
H19 is able to produce its own necessary energy. H19 is able to produce its own
necessary energy; in this way LCC remains constant with energy prices. The
descendent trend with the factor of variation of the price of energy is ascertained in
cases of H22 and H25 that are Plus-Energy houses able to export their surplus.
a)
b) c)
d) e) Fig. 7 Specific Space Life Cycle Cost (LCC) with sensitivity analysis
Net Savings shew a similar trend of variation for H16, H19, H22, H25 when
the price of energy is taken into consideration, but mention must be made of an
increase of the values by accentuating the negative price escalation factor of the PV
panels. The range of the values is radically influenced by the price of PV panels,
especially for Plus-Energy houses.
The Adjusted Internal Rate of Return, AIRR is applicable especially when the
investment is made by a company, but in any other situation it is a rigorous
parameter for the determination of the efficiency of a project and has to be as high
as possible in comparison with the rate of discount.
In general, the rate of discount used in calculations in projects is of 3% and
in the case of analyzed houses the values of the AIRR of 4-4.5% are obtained, a
percentage which is higher than the base value. For the domestic projects of natural
persons, this rate value is reasonable, but for companies it is still low, but at least it
meets the minimum requirements.
In order for these projects to be much more appealing, besides the gains
arising from improving the efficiency, they should also be able to obtain a certain
quota of the initial investment from authorities.
An important evaluation involves Discounted Pay-Back Time (DPBT) (fig.
8) which is determined by people’s tendency to recover as quickly as possible the
extra charges added to an investment. After this period, when the value is recovered,
a remanent time is considered when the benefits arise from the full ownership of
the project which eventually became free of arrearages.
a)
b) c)
d) e)
Fig. 8 Discounted Pay-Back Time (DPBT) with sensitivity analysis
Table 8 shows the global situation of the additional investment specific for
the houses H13-H25; it also shows five decision criteria through a simple
classification system where the best project receives 14 points and the worst 1 point.
In addition, a global classification that integrates all 5 criteria gives an overview on
the economic sustainability of the project. The terms of the pair LCC and NS, SIR
and AIRR correlate as score with 100%, while DPBT has a nonlinear dependence
on NS. The economic techniques make it possible to obtain final results that are
able to simplify the decision through rigorous algorithms while uncertainty is
reduced.
Table 8 Overall balance and ranking of the additional investment solutions
Minimum
Inv Minimum LCC
Maximum
NS Maximum SIR Maximum AIRR Minimum DPBT
Overall
Classif.
Value
[Euro/m2]
Score
(Rank)
Value
[Euro/m2]
Score
(Rank)
Value
[Euro/m2]
Score
(Rank)
Value
[-]
Score
(Rank)
Value
[-]
Score
(Rank)
Value
[Years]
Score
(Rank)
Score
(Rank)
H12 707.8 14(1) 1178.4 1(14) 0.0 1(14) 0.0 1(14) 0.000 1(14) 30 14(1) 32 (13)
H13 869.3 13(2) 1083.6 4(11) 94.8 4(11) 1.6 10(5) 0.046 10(5) 20 9(6) 50 (6)
H14 875.2 12(3) 993.1 11(4) 185.3 11(4) 2.1 14(1) 0.056 14(1) 16 3(12) 65 (1)
H15 974.1 9(6) 1095.0 3(12) 83.4 3(12) 1.3 5(10) 0.039 5(10) 24 12(3) 37 (10)
H16 926.0 11(4) 1045.5 7(8) 132.8 7(8) 1.6 11(4) 0.046 11(4) 20 9(6) 56 (4)
H17 946.9 10(5) 1011.6 9(6) 166.8 9(6) 1.7 13(2) 0.048 13(2) 18 5(10) 59 (2)
H18 1045.9 6(9) 1113.5 2(13) 64.9 2(13) 1.2 2(13) 0.036 2(13) 26 13(2) 27 (14)
H19 997.8 8(7) 1064.0 5(10) 114.4 5(10) 1.4 6(9) 0.041 6(9) 21 11(4) 41 (9)
H20 1018.7 7(8) 962.0 12(3) 216.4 12(3) 1.7 12(3) 0.048 12(3) 16 3(12) 58 (3)
H21 1117.7 4(11) 1063.9 6(9) 114.5 6(9) 1.3 3(12) 0.038 3(12) 21 11(4) 33 (12)
H22 1069.6 5(10) 1014.4 8(7) 164.0 8(7) 1.5 8(7) 0.043 8(7) 19 7(8) 44 (8)
H23 1234.1 3(12) 894.9 14(1) 283.4 14(1) 1.5 9(6) 0.045 9(6) 16 3(12) 52 (5)
H24 1333.0 1(14) 996.8 10(5) 181.5 10(5) 1.3 4(11) 0.039 4(11) 19 7(8) 36 (11)
H25 1285.0 2(13) 947.4 13(2) 231.0 13(2) 1.4 7(8) 0.042 7(8) 18 5(10) 47 (7)
The criterion of initial investment (Inv) obviously brings the choice of H12
(the base case or standard solution) as the cheapest solution and disagrees the most
with H24 (with GHPx2 and PVx5), which is the most expensive. The life cycle cost
LCC and net saving NS recommend H23 solution which gives a combination of a
relatively cheap investment in EAHXx2 system coupled with the version of most
PV panels (PVx5) that significantly reduce the final cost by producing and selling
electricity. Parameters SIR and AIRR recommend the cheapest solutions H14, H17
and reject H18. However, an overall comparison recommends solutions H14, H17
and H20.
7. Discussion
A fact to be discussed is that the solutions Plus-Energy are not placed on the
top of the list and an explanation can be found for this. The costs for PV panels are
still big as initial investment. An encouraging fact is that most companies that invest
in renewable energy systems obtain from the Government of their country apart
from operating subsidies, also non-reimbursable credits that cover totally or
partially the initial investment in PV panels or renewable energy systems. Many
investments in the European Union have compensations of 50% or even 100% if
they are made in the field of renewable energy. A separate study can be dedicated
to the impact that certain facilities granted at the European or national level can
have, but it is appreciated that if the initial investment was compensated by 50%
then the Adjusted Rate of Return would increase to values above 7.5% in the
assessment of 30 years, a value which would meet even the usual exigencies of the
commercial companies.
One thing that may not be predictable is the fact that governments change and
financing policies can be significantly affected. The latter will still exist, under the
form of facilities granted for sources of renewable energy, considering that every
EU country has important objectives related to sustainable development.
A sensitivity analysis involving a reduction in the cost of the initial
investment in PV panels is needed; the state can give grant funds for the initial
investment, and this can be a topic for future analysis. An inverse problem can also
be formulated: how much of the initial investment should be covered by grant funds
in order for investors to consider it a really attractive business? Anyway, in this
study we presented investments based on the real market, investments that show
that throughtout the life cycle of 30 years the initial investment is recovered and
positive net savings are obtained.
Another problem is the high variability of the price of investment from
country to country depending on that country's policy for renewable energy. This
variability can easily reach 30%, compared to the average acquisition cost for
countries with market economies. This issue can also be studied; such a study
should aim at establishing what list of countries from trade statistics for investment
may be preferred, given several initial requirements. By using the published
statistics, comparative studies can be made for EU countries; for example, 3-5
countries involving a variety of prices for equipments, energy - this is a kind of
analysis made by international corporations when they study the possibilities of
investment in some countries and choose the best for a given opportunity.
Sometimes, on short term, investors look for answers to the question whether it is
sustainable to invest at present in a given country or to wait for 1-2 years for a
predicted improvement of the economic conditions. Clearly, in order to achieve a
level of efficiency sought by companies (in which AIRR ≥ 7.5%) partial or total
grants for specific equipments of production of clean and renewable energy are
required.
8. Conclusions
This paper reproduces the economic model of the Passive House
POLITEHNICA of Bucharest at the parametric level; the latter allowed subsequent
technical variations by adding and removing equipments that affect the final energy
consumption.
The software CYCO-PH was built at University POLITEHNICA during
this study. This software is specialized in analyzing heterogeneous solutions of
investment projects in buildings that include renewable energy systems, particularly
PV panels for the production of electricity, solar collectors, heat pumps, etc.
A comparative analysis of a range of solutions of houses, among which are
a standard house (H12) and the Passive House POLITEHNICA (H19), was made
by means of several criteria of cost that are significantly influenced by energy
efficiency. All these criteria were finally abstracted in a classification system that
helps investors to choose the best solution for their purpose.
We concluded that the recovery of the additional investment in alternative
and energy-efficient solutions in comparison with a standard house can be achieved
in 16-33 years by a conservative assessment or in 16-26 years when the best
forecasts of the economic conditions are considered.
The base case itself influence accordingly the results of evaluation: if
standard house have the solution of heating and DHW based on gas fuel then
payback time is achieved in 16- 26 years; if heating and DHW is based on electricity
then payback time is achieved in 9-16 years; if heating and DHW is based on
District Distribution then payback time is achieved in 16-28 years. As noted, the
District Distribution system remains the most difficult to be replaced by renewable
energy systems applied to the buildings.
The sensitivity analysis with the deterministic approach has imposed
scenarios of variation from the uncertainty of the economic environment, sketching
possible ranges for the monitored parameters (LCC, DPBT). This analysis can be
completed in the future through an approach that includes risk analysis.
The price variations from country to country and also from year to year are
wide (for renewable energy systems in general and for PV panels in particular) and
this can be a special research topic.
Beyond the interpretation of the results of this research paper, every investor
may prepare its own decision based on its goals. The life-cycle cost method used in
this study was able to provide useful information and a new approach to potential
investors (individuals, institutions, companies) that can be used in their projects.
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