Proceedings of the 13th International Conference of Environmental Science and Technology
Athens, Greece, 5-7 September 2013
A COMPARISON OF THE ECONOMIC SAVINGS BETWEEN THERMAL
SOLAR SYSTEMS AND THERMAL INSULATION IMPROVEMENTS FOR
SOCIAL HOUSING IN CHILE
M. PILAR GARATE * and PEDRO M. GURIDI *
*Universidad Técnica Federico Santa María
Av. Santa María 6400, 7660251, Santiago, Chile.
[email protected]
ABSTRACT
Chilean´s energy matrix is mainly based on fossil sources. The lack of natural resources
and increasing international prices has forced the state to promote the use of renewable
energy sources and to implement a national energy efficiency program. In this context, in
2009 a law was promulgated that promotes the use of thermal solar systems in social
housing granting a tax discount to those companies that incorporate this technology. As a
consequence of this law, thermal solar systems have been installed in more than 600
social houses during 2012, distributed in projects throughout the country, and it is
expected that in 2013 this number will increase to approximately 1500.
The present work analyzes the economic effects on the energy consumption in social
housing of the thermal solar systems and compares them with improvements in thermal
insulation. The objective is to evaluate the effectiveness of public policies orientated to
social housing.
The savings due to thermal Solar System were calculated using the so-called f-Charts.
Those charts allow estimating the percentage of the energy required to satisfy the
demand of the family for sanitary hot water that can be provided by the thermal Solar
System. A comparison for a period of evaluation of 20 years was made between the case
with and without the thermal Solar System. These savings were compared with the ones
obtained considering a higher standard than the Chilean norm for thermal insulation in
floor, ceiling, walls and the replacement of glass by double hermetic glass. The
calculation of the necessary heat flow for heating was obtained using the method of
circuits of thermal resistances.
Although the incorporation of thermal solar system in social housing is an effective
measure to reduce energy consumption, the economic savings are greater when a higher
standard of thermal insulation is applied, particularly the incorporation of double hermetic
glass windows. The savings are even greater if higher prices of the heating fuel are
considered. From the results we infer that a deep analysis of public politics oriented to
social housing regarding energy efficiency should be carried out. The possibility of
subsidies to insulation needs to be analyzed in detail.
KEYWORDS: Thermal Solar System, Insulation, Social Houses, f-Charts, Circuits of
Thermal Resistances, Double Hermetic Glass.
1 INTRODUCTION
During the past few years problems such as greenhouse effect, global heating, historical
housing deficit and increasing international energy prices, have forced the Chilean state
to implement energy efficiency policies [1]. Being social housing one of the most sensible
areas, many efforts have focused in the development of green and sustainable social
housing. The most recently is a law promulgated in 2009 that grants a tax discount to
those companies that incorporate thermal solar technologies in their projects. However
there are other strategies for reducing energy consumption that have not been
considered. The main drawback in the implementation of energy efficient housing is the
high initial investment due to the specificity of the required materials and its high cost in
the Chilean market.
Since its publication approximately 600 families have benefited from the incorporation of
solar thermal systems in their homes, and it is expected that at the end of 2013 will
benefit another 900 families. Using the so-called f-charts the energy savings of a
particular house can be estimated. As mentioned before, other strategies such as
improvement of thermal insulation need also be considered in a global analysis of a
energy efficient housing design. The methodology used to determine these savings
corresponds to the thermal resistance circuits. The comparison between both results
seeks to determine which of the measures is more effective and should have a greater
impact on energy and heating costs savings. In order to validate the study data of local:
temperature, solar radiation, demand of hot sanitary water and energy required for
heating corresponding to a social house located in the commune of Lo Espejo [2,3] in
Santiago, Chile, were used.
2 METHOD OF F-CHARTS
Construction companies in Chile can only make use of the tax discount if they are able to
demonstrate, by calculation reports, that the contribution made by the thermal solar
systems meet at least 30% of the average annual hot sanitary water demand.
Additionally, they must be registered in the list of the Electricity and Fuels goverment
office. By Thermal Solar System it is understood a system that “Integrates a Thermal
Solar Collector, Accumulating Tank and a set of other components responsible to make
the functions of capturing the solar radiation, transform it directly into thermal energy,
which is transmitted to a work fluid, and finally to store this thermal energy either in the
same working fluid or another, to be used in the points of hot sanitary water
consumption”. That system needs to be supplemented with a conventional heating water
system; however, it is not considered part of the Solar Thermal System [4-8]. The first
part of the calculations corresponds to determine the solar energy available for each
month, depending on the average daily global solar radiation, the number of days of the
month, the orientation of the solar collectors and the shadow losses [9,10]. The second
part consists of calculations of the amount of monthly energy needed to meet the demand
of hot water that depends on: the consumption by person, the number of residents, the
temperature of the water in the pipes, the area of the collectors, the optical efficiency of
the system and the volume of hot water storage. With these data we obtain the “relation
between absorption and energy demand” and the “relation between losses and energy
demand” for each month. We weighted and normalized these relations to determine the
percentage of energy that is able to meet the solar thermal system, that is the annual
solar contribution. Finally, the ratio between the calculated annual solar contribution and
the annual energy demand gives the percentage of solar contribution. In figure 1 it can be
seen that except for winter months, the thermal solar system may provide all the required
energy for hot sanitary water production.
600.00
500.00
400.00
300.00
200.00
Demand [MJ/month]
100.00
Input [MJ/month]
January
February
March
April
May
June
July
August
September
October
November
December
0.00
Figure 1. Supply and demand graph of solar energy.
3 PROPOSAL OF OPTIMAL INSULATION
Chilean Thermal Regulations establish the maximum acceptable thermal transmittances
for housings depending on the temperature zone where are located [11]. First, the
thermal transmittance circuit for a real social house was calculated (see fig.2) [12-15]
which is essential to determine the heat losses of the housing. Thermal transmittances
depend of factors such as: characteristics of the materials, disposition in the housing
(series or parallel) and convection coefficient. The same calculation was also made for
the constructive elements selected for extra insulation. Those materials, Polystyrene
Expanded (EPS) and doble-pane (insulated glazing), were selected according to an
economic balance between investment and heat losses. With the complete thermal
transmittance circuit the heat losses were estimated. Considering the energy cost and the
fact we are studying a social housing, a heating technology that uses kerosene as fuel
was selected to provide the power necessary to compensate the calculated heat losses.
With all these data we carried out an economic analysis varying the thickness of the
insulation.
Figure 2. Thermal Transmittance circuit for housing floor. In red is shown the circuit with
the extra insultation.
The optimal level of insulation was found minimizing overall costs in the long term to
achieve thermal comfort during the project life cycle. As it can be seen in figure 3, the
optimum solution corresponds to a level of extra EPS insulation of 50 [mm] in ceiling, floor
and walls and the installation of doble- pane in windows.
$ 3,500,000
$ 3,000,000
Costo [$]
$ 2,500,000
$ 2,000,000
$ 1,500,000
$ 1,000,000
$ 500,000
$-
Heating Cost [$]
Additional Investment [$]
Total [$]
Figure 3. Heating cost, Additional investment and total cost.
4
RESULTS
4.1 Comparison between proposals
Making a comparison between both proposals it can be concluded that the proposed
improvements in housing insulation present a better energy and economic savings. The
results are resumed in table 1. Nevertheless, both measures could be adopted if the
appropriate incentives for construction companies are implemented. The Thermal Solar
System saves USD 2,000 for a period of evaluation of 20 years approximately, while the
proposal of additional isolation saves USD 3,000 for the same period approximately.
Table 1: comparison of thermal solar system and insulation improvement.
Thermal solar system Insulation improvement
Savings (NPV)
USD 2.000
USD 3.000
IRR
21,83%
46,57%
Payback
6 years
3 years
Cost reduction
51,35%
55,70%
Among the factors affecting the economic convenience of improved insulation for housing
we must mention the energy demand, determined by weather conditions (expressed in
terms of temperature) and the length of days of use, the technology used for heating and
the value of the kilowatt-hour of fuel, aspects of architecture, design and construction and
materials selection, selection of construction techniques, housing design, housing
condition (isolated, twin or continuous), orientation of the glass surfaces, avoid
unnecessary thermal bridges and ultimately the type of selected additional insulation. The
highest the demand of energy for heating more convenient is to implement this proposal.
4.2 Housing form factor
The Economic evaluation carried out to verify the suitability of the proposed
improvements in insulation responds to the particular conditions of the studied house, i.e.,
its design, surface and location. To apply the same evaluation for different types of
housing a form factor would be calculated that allow counting for different types of
housing.
The form factor of a housing is a geometric relationship between volume enclosing
habitable housing and exposed surface. As the heat losses are proportional to the
exposed surface this is an important factor for determining the thermal behavior of the
housing. The exposed surface is related to the condition of the house and outbuildings.
To calculate this factor it is necessary to determine the amount of housing space and its
weighted thermal transmittance (Uweighted).
𝑈𝑤𝑒𝑖𝑔ℎ𝑡𝑒𝑑 =
𝐹𝑜𝑟𝑚 𝐹𝑎𝑐𝑡𝑜𝑟 =
∑𝑖 𝑈𝑖 ∗𝐴𝑖
∑ 𝑖 𝐴𝑖
(Eq. 1)
𝑈𝑤𝑒𝑖𝑔ℎ𝑡𝑒𝑑∗𝐴𝑒𝑥𝑝𝑜𝑠𝑒𝑑
𝑉ℎ𝑎𝑏𝑖𝑡𝑎𝑏𝑙𝑒
(Eq. 2)
The form factor calculated using equation 2 is then normalized considering the original
housing design. Then this form factor is used to modify the energy demand for heating of
housing with different geometrical dimensions but same habitable volume. In table 2 are
shown the normalized form factor for different housing conditions (see fig. 4).
Figure 4: Isolated, twin and continuous housing.
Table 2: Normalized form factor for different housing conditions.
Original design Regular one floor Regular two floors
Continuous
1
0,99
0,71
Twin
1,21
1,11
0,88
Isolated
1,33
1,23
1,05
The better the normalized form factor of a housing, the worse performance in terms of
energy and cost savings, i.e. generate greater savings for housing with worse form factor.
Although economic performance was lower in housing with good form factor these
savings remain still important and attractive as is shown in table 3.
Table 3: IRR for different housing conditions.
Original design Regular one floor
Continuous
46,57%
46.18%
Twin
56,60%
50,01%
Isolated
62,50%
53,59%
Regular two floors
36,26%
42,50%
48,16%
5 CONCLUSIONS
In the present work it has been shown that installation of thermal solar systems and
improvements in thermal insulation in social housing will result in energy and heating cost
savings. However, the combination of extra insulation and doble-pane generates higher
economic savings. Consequently, it should be necessary to consider a revision of the
thermal transmittance regulations. It is important at this point to mention that an
improvement in thermal insulation not only generates energy and heating cost savings
but also improves the quality of life of the people living in those houses. Better thermal
comfort in summer days, extra acoustic insulation, better quality of the air in winter days
are some of the extra benefits.
The implementation of energy efficiency measures and innovation in residential dwellings
would comply with the requirements associated with the concept of self-sustainable
housing.
Finally, in terms of public policies it should be mandatory to carried out a general analysis
of the energy efficiency measures apply to social housing in order to promulgate laws that
may result not only in energy and heating cost savings but also in a significant
improvements of the quality of life of the most vulnerable population. Particularly in that
case, it should be advisable to modify the thermal transmittance national regulations and
also incorporate tax discount for companies that incorporate doble-pane in their social
housing projects.
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