ISSUE27!!|!!October!!2017 · 2017. 11. 6. · !!!!!ESPAÇO!ENERGIA!!| !!!ISSUE27!!|!!October!!2017...

ESPAÇO ENERGIA | ISSUE 27 | October 2017

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Energy and monetary payback time of rockwool as an insulation material in the retrofit of buildings in the temperate climate zone in Brazil

Tempo de retorno energético e monetário da lã de rocha como material de isolamento térmico no retrofit de edifícios na zona de clima temperado do Brasil

Aloísio Leoni Schmid [email protected] Ricardo Cezar Mello Mattos Habib [email protected]

Universidade Federal do Paraná – UFPR Programa de Pós-‐Graduação em Engenharia de Construção Civil

Abstract: This paper aims at raising more detailed and specific data on the embodied energy of rock wool, in low density, 5 cm-‐thick mats, and also at calculating the payback time of rockwool as the main material of the retrofit of a social house in Curitiba, Brazil. Five scenarios (A to E) were established. Scenario A is a baseline of the embodied energy and costs. Each variation on the

scenarios B, C, D and E had its increased embodied energy and costs calculated and simulated to obtain the operation energy. It was observed that the retrofit with rockwool produced savings on heating and cooling costs despite an increase in embodied energy. Therefore, the payback time of the investment in each scenario was calculated.

Keywords: Thermal insulation materials; embodied energy; building thermal simulation; energy retrofit.

Resumo: Este artigo visa a levantar dados mais detalhados e específicos sobre a energia incorporada de lã de rocha, de baixa densidade, mantas de 5 cm de espessura. Calcula também o tempo de retorno da lã de rocha como o principal material do retrofit de uma casa com projeto de interesse social em Curitiba, Brasil. Foram estabelecidos cinco cenários (A a E). O cenário A é a linha de referência da energia incorporada e dos custos. Cada variação nos cenários B, C, D e E teve seu aumento de energia incorporada e custos calculados e simulados para obter a energia de operação. Observou-‐se que o retrofit com lã de rocha produziu economias em custos de aquecimento e refrigeração, apesar do acréscimo na energia incorporada. Portanto, calculou-‐se o tempo de retorno da operação em cada cenário.

Palavras-‐chave: materiais de isolamento térmico; energia incorporada; retrofit energético.

1 Introduction

Brazil is mainly a tropical country; however, it includes at least nine climate zones according to the national standard ABNT 15220. One of them, the so-‐called Bioclimatic Zone 1, is a temperate zone, and more than half of its population lives in the metropolitan region of Curitiba, capital to the State of Paraná. The city has latitude 25°S and longitude 45˚W, and at an altitude higher than 900 m, on the first of three highlands, which make out most of the territory of the state. Climate is highly humid throughout the year; summers are moderate, with absolute maxima mostly under 30˚C; in winter, absolute minima below 0˚C are not rare. The city of Curitiba presents 26,000 yearly degree hours for heating at 18˚C, ranging from 377 degree hours in February to 4,473 degree hours in June, and only 780 yearly degree hours for cooling at 26˚C, which are negligible in May, June and July. The population has a relevant share of descendants of immigrants from cold countries like Poland, Germany, Italy, Ukraine and Japan, who combined original and adapted vernacular elements in their houses. However, such buildings reflected an original condition of temporary rural settings, which were rather poor.

Brazil experienced an intense urbanization and the real estate business left behind most technological contributions by the immigrants. The current building industry resembles nowadays what is built in the majority of the country: a reinforced concrete structure; external walls most frequently 12 cm thick, made of


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hollow ceramic bricks and a mortar finish; single-‐glazed windows; concrete slabs laid on the ground or over garage space, with no thermal insulation; ceramic or fibrocement roof tiles with no thermal insulation. In the last 20 years, radiant barriers have become more frequent.

The search for thermal comfort in buildings, associated or not with the care for keeping operation energy (OE) costs low, may encourage the building retrofit. One representative situation is the case of a single building, what matters is the point of view of the owner, who compares costs and benefits. Another is the case of a public policy to promote the retrofit of a number of building units. That choice cannot be only a matter of scale as, beside costs and benefits, there are inputs and outputs, and a whole energy balance involved. The embodied energy (EE) of the retrofit, which may appear as an external cost to the single owner, becomes an explicit cost to society.

Thermal insulation is one of the most effective forms of energy saving used for heating and cooling buildings. In a moderate climate, heating the air inside buildings, especially in the winter, but also in transitional periods (autumn and spring) is significant as the demand for thermal energy is needed. Therefore, the determination and choice of the best insulation thickness is the main objective of many research projects [1].

In many countries, the energy consumption of buildings is around 40% of global energy demands and the energy requirement for heating and cooling a building is approximately 60% of the total energy consumed in buildings, which represents the largest percentage of energy use [2].

In 2001, the United States consumed 18.6 EJ of energy in the residential sector and was responsible for the emission of 1,155 Gt of CO2 [3]. These figures represent about 18% of energy needs and 20% of national CO2 emissions [4].

Heating and cooling accounted for 41% of the primary energy used and 36% of the CO2 emissions in the residential sector, representing in both cases around 7% of the national values in that country. While the importance of residential heating and cooling is well understood, less obvious are the environmental impacts associated with the manufacturing process and the transportation, recycling or disposal of materials used in construction, renovation and maintenance [5].

During the first decade of the 21st century, energy consumption has been increasing rapidly due to increasing population growth, urbanization, migration to large cities and improved quality of life. This consumption is distributed among four main sectors: industrial, construction (residential / commercial), transport and agriculture [6].

When the building thermal load is mainly a heating load, classic solutions to reduce the operation energy costs are:

a) improving the thermal resistance of the envelope;

b) minimizing the ventilation air flow, or the implementation of heat recovery in the ventilation system; and

c) improving solar direct or indirect gains.

Ventilation becomes relevant in buildings that have an already efficient envelope. The increase of solar gains, usually accomplished by the attachment of greenhouses to the facade, might be a more difficult task.

Both solutions are of relatively low impact in terms of added materials and increase of embodied energy. However, most probable is that the increase of thermal resistance has a higher impact in the reduction of energy consumption, particularly when the building envelope was not designed for the whole year climate conditions. This choice may be associated with a relevant impact in embodied energy.

When the building thermal load is mainly a cooling load, classic solutions are:

a) blocking solar radiations through roof and aperture;

b) improving ventilation, preferring cross-‐ventilation to chimney effect;

c) increasing the thermal resistance of the envelope at the surfaces that are most critically hit by the sunshine like west-‐facing walls, or along the whole building envelope in the case of night ventilation, or mechanical cooling.

In a temperate climate, the latter choice agrees with the situation of prevailing heating loads. Shadow can be achieved, also, by means of vegetation: deciduous trees are to be preferred; green walls and green roofs add heat capacity and an evaporative effect. The increase of heat capacity in order to diminish the thermal amplitude of the internal amplitude might be not feasible due to structural restrictions.

Considering that the increment of thermal resistance of the building envelope is a solution for both situations of prevailing heating and cooling loads, and that it has an expected impact in embodied energy [7], such technological solution requires a closer examination. It encompasses both opaque and transparent parts of the envelope.

Transparent elements and framing are usually much thinner than opaque elements, giving rise to thermal bridges which, according to the transparent to opaque ration of envelope area, may become relevant.

Opaque elements usually cover a much wider envelope area and are much thicker than transparent elements, possibly becoming the most influential item in the energy


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payback calculation. Most common thermal insulation choices for opaque parts include natural materials (cork, coconut fibre, cotton and wool); processed mineral materials (glass wool, rock wool, vermiculite and perlite); synthetic materials (EPS, EPU).

Rock wool is described by [8] as a mostly grey or olive green coloured material, which has a use as a thermal insulation, or in the protection against fire and also in the acoustic insulation. It is less flexible than glass wool, which provides it with a better behaviour in the assembly of wall panels. The same reference mentions an embodied energy of 13 MJ/kg (this value was obtained mainly from German companies).

Rock wool presents most advantages over other insulation materials: it is durable, non-‐biodegradable, non-‐inflammable and non-‐toxic and made of abundant raw materials. Its costs are close to most alternatives as EPS or glass wool. However, the manufacture of rock wool requires high temperatures, which leads one to expect an impact on energy consumption. As the final product is voluminous, it limits the carrying capacity of trucks, so that an impact of the transportation energy is also expected. However, literature indicates a favourable payback time in some applications [9, 10, 11, 12, 13].

The present work has two purposes. First, to raise more detailed and specific data on the embodied energy of rock wool in low-‐density, 5 cm-‐thick mats, as transported to Curitiba, in the temperate climate zone in Brazil. In order to do that, authors visited the main factory of the product in Brazil. Second, to calculate the payback time of rockwool as the main material to the energy retrofit of a social housing unit in same city. The house was modelled and simulated as to its thermal behaviour considering the temperate, super humid climate, with moderate summer temperatures, and a cold winter with heating load along about two months a year.

This study contributes to the research on energy efficiency in buildings highlighting the implementation of a rock wool-‐based thermal insulation in walls and ceilings as one of the ways to improve this efficiency. As an innovation, this study also considerd the initial energy (IE) and its trade-‐off with operation energy (OE)

Starting with a standard house (scenario A) in Curitiba, in a temperate climate (bioclimatic zone 1), whose envelope presents a lacking thermal resistance, a payback time shorter than one year was obtained in all scenarios B, C, D and E.

Furthermore, although studies show that the IE for rock wool production in Brazil is similar to that spent in the USA, the Brazilian energy matrix is almost entirely from renewable sources, unlike the U.S. energy matrix that is based on non-‐renewable energy.

The city of Curitiba has population over 1.7 million inhabitants, which gives the problem a quantitative relevance [14].

2 Materials and Methods

The determination of the embodied energy of rock wool required, first, bibliographic and documental research.

Next, authors visited a factory of the main manufacturer of rock wool in Brazil and could observe all production steps and interview the Company CEO in order to verify the conformity of the literature and the actual practice.

Once the value of embodied energy of rock wool (specifically, for a low-‐density, 5 cm-‐thick mat) was obtained, the three-‐dimensional model of the house was developed and four retrofit scenarios of addition of new materials were considered.

Transportation energy of new materials to the building site was considered.

Operation energy consumption was calculated from a thermal simulation of the building thermal performance according to the climate data of Curitiba.

2.1 Addition of thermal insulation

In order to determine the embodied energy of rock wool, authors first considered basic information from the North American Insulating Material Association -‐ NAIMA [15]. The interview with the company CEO can be found in [12].

The NAIMA survey demonstrates that the production of 1.00 m2 of rock wool mat weighting 3.36 kg requires as raw materials 1.10 kg of basalt rock, 1.29 kg of sludge obtained from the production of iron, silicon and manganese alloys, 1.32 kg of water and 1.43 kg of residues. As energy sources, there is the consumption of 16.90 MJ of coal (to melt the rocks in the cupola oven), 7.68 MJ of natural gas (to provide heat to the process of curing and also for the product wrapping), and 3.87 MJ of electric energy (to power the conveyor belt) considering a 100% efficient power plant. Therefore, the energy consumption is 8.467 MJ/kg or 569 MJ/m3, or 28.4 MJ/m2 of the 5 cm-‐mat.

NAIMA survey 2.1.1

Figure 1 illustrates the production process of rock wool.

Figure 1: Scheme of rock wool production [16].


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Visit to Rockfibras 2.1.2

In September, 2013, the authors visited the Rockfibras Company, 100 km Northeast from São Paulo. The visit allowed them to follow each step of rock wool production and confirm the information found in the NAIMA Report [15]. Figures 2 to 4, by the authors, illustrate part of the production process.

According to the Company, the energy consumption needed to produce 1 kg of rock wool is 2,349 kcal/kg or 2.73 kWh/kg. That value comprehends coal (70%), BPF oil (14%), diesel oil (6%) and electric energy (11%). Diesel costs are due to the transportation of raw materials to the factory. There is a specific consumption of 9.828 MJ/kg, or 660 MJ/m3, or 33.0 MJ/m2 for the 5 cm-‐thick rock wool mat.

Figure 2: General Prospect [9].

Figure 3: Output of melt rock on the conveyor belt. [9].

Figure 4: Cutting the mat to the final width [9].

A critical analysis of those data would take the electric energy consumption as obtained by a 27.5%-‐efficient plant to convert heat into electricity. The result would be higher 12.678 MJ/kg, 852 MJ/m3, or 42.6 MJ/m2 of the 5 cm-‐thick mat.

Considering the construction site in Curitiba, 500 km from the factory, and the specific consumption of 3.56 MJ/km/t on a 28 t-‐truck, according to the comprehensive ecological inventory by IFIB [17] apud [18], one gets 76.74 MJ/m2 of rock wool mat.

2.2 Building evaluation

Does it make sense to adopt rock wool in an energy retrofit action? A quantitative evaluation requires a defined geometry, which will influence the energy embodied in the necessary materials, as well as the thermal behaviour and consequently the operation energy consumption. As a representative case, a standard low-‐income, single family house known as R1B, as described by the Brazilian Standard ABNT 12721, which establishes a national cost index, was adopted [19]. Figure 5 depicts the plan of the adopted design.

Figure 5: Plan, R1B design– NBR 12721 [19].

Building description 2.2.1

The building under analysis is single-‐floor and consists of following materials:

! 11 cm-‐thick walls made of 9 cm-‐wide hollow bricks, 1 cm of mortar and paint outside, and 1 cm of gypsum and PVA paint inside;

! aluminium frames and single glass panes, 4 mm-‐thick;

! 35 mm-‐thick wooden doors; ! 10 cm-‐thick concrete floor slab on piers, and

1 cm-‐thick ceiling of light timber; ! ceramic roof tiles, 1 cm-‐thick, on timber

structure.

2.3 Determination of cost and embodied energy

Scenario A was taken as baseline of both embodied energy and costs. Each variation B, C, D and E had its increased embodied energy and costs calculated, and was simulated to obtain the operation energy.


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2.4 Pre-‐operation energy

The embodied energy was calculated having as main reference [18], which is a study of embodied energy of the R1B house model. The transportation component of embodied energy was corrected considering the construction site in Curitiba.

2.5 Pre-‐operation energy in construction materials

Scenarios A to E are shown in Table 1. Added construction costs are shown in Table 2. All costs are in US$ and use metric notation. The average exchange rate (R$ to US$) for February of 2015 was considered [20]. Table 1: Pre-‐operation energy, scenarios A to E [9]. Scenario A – baseline

Total (MJ) Total 0.00 Scenario B – Addition of rock wool (5 cm) and gypsum (1cm) at inner face of exterior walls [9].

Volume (m3) EE (MJ/m3) Total (MJ)

Total Scenario A 0.00 Rock wool 50 mm 2.7063 1,475.00 3,991.79 Gypsum plasterboard 0.5607 5,400.00 3,027.78

Galvanized profile 48 mm x 29 mm 0.0072 265,330.00 1,910.38

PVA paint 0.0097 84,500.00 819.65 Total 9,749.60 Scenario C – Addition of rock wool (5 cm) on the ceiling [9].


Total Scenario B 9,749.60 Rock wool 50 mm 2.2340 1,475.00 3,295.22 Total 13,044.82 Scenario D– double glazing (8mm + 8mm + 6mm). [9]


Total Scenario C 13,044.82 Wooden frames -‐0.0439 2,100.00 -‐92.19 Single glazing 3 mm -‐0.0230 46,250.00 -‐1,063.75

Aluminium frames 0.0078 567,000.00 4,422.60 Double glass 8+8+6

0.10752 46,250.00 4,972.80

Total 21,284.28 Scenario E– Addition of rock wool (5 cm) under the floor slab, with gypsum plasterboard [9].


Total Scenario D 21,284.28 Rock wool 50 mm 2.23405 1,475.00 3,295.22 Gypsum plasterboard 0.5607 5,400.00 43,027.78

Galvanized profile 48mm x 29mm 0.0072 265,330 1,910.38

Total 29,517.66

2.6 Operation energy

A three-‐dimensional model of the RB1 house was built, as depicted in Figure 7, and simulated as to its thermal behaviour using the Mestre simulation system.

Mestre considers a building as a thermal model of lumped masses representing multiple zones with a realistic geometry for consideration of solar radiation by means of a numeric approximation.

The standard year is discretized in time steps of one hour in an unsteady-‐state thermal transfer analysis.

Table 2: Added construction costs [9]. Scenario A – baseline

Total (US$) Total 0.00 Scenario B – Addition of rock wool (5 cm) and gypsum (1cm) internally to exterior walls [9].

Area (m2) Costs

(US$/ m2) Total (US$)

Total Scenario A 0.00 Rock wool 50 mm 54.27 4.50 244.22 Gypsum plasterboard 54.27 23.24 1,261.13

Galvanized profile 48mm x 29mm 54.27 10.42 565.49

PVA plaster 54.27 0.63 34.19 Total 2105.13 Scenario C – Addition of rock wool (5 cm) on the ceiling. [9].

Area (m2) Costs


Total Scenario B 2105.13 Rock wool 50 mm 44.68 4.50 201.06 Total 2,306.19 Scenario D– double glazing (8mm + 8mm + 6mm)

Area (m2) Costs


Total Scenario C 2,306.19 Wooden frames 7.680 -‐83.30 -‐639.74 Single glazing 3 mm 7.680 -‐11.44 -‐87.89

Aluminium frames and double glazing

7.680 502.28 3,857.55

Total 5,436.10 Scenario E– Addition of rock wool (5 cm) under the floor slab, with gypsum plasterboard [9].

Area (m2) Costs


Total Scenario D 5,436.10 Rock wool 50 mm 44.68 4.50 201.60 Gypsum plasterboard 44.68 23.24 1,038.36

Galvanized profile 48mm x 29mm

44.68 10.42 465.57

Total 7,141.09


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Figure 6: Simulation model. Render by Mestre [21].

Fences, trees or other shadow-‐casting elements were not included. The house main facade was oriented to the west. The effect of building orientation on the operation energy consumption was not considered, as apertures are almost equally distributed between different facades and the roof offers protection against critical solar radiation. A clockwise rotation of 90˚ produced no relevant difference in the energy consumption. Therefore, only the orientation with the main facade to the West was considered. The simulation system had its development started in 2001 by the first author, using the Java language.

First, the thermal analysis module was developed. Results of that analysis are either the zone temperature

marches for non-‐conditioned buildings, or the marches of heating and cooling power values at each zone in the case of mechanically conditioned buildings. Later, a module for the simulation of light propagation by a combination of raytracing and radiosity method was added.

Besides isolux lines, realistic imagens in three-‐point perspective and fish-‐eye view can be obtained. Later, a room acoustics module was also added, including the possibility of auralization (acoustic rendering of anechoic files according to the numerically calculated impulse response of the room). The thermal analysis module was tested under the International Energy Agency IEA BESTEST procedure for multiple zones, non-‐airflow buildings and yielded trustable results [21].

The physical properties of the materials influencing the thermal behaviour of the building are listed in Table 3.

Table 4 presents zone ventilation rates (m³/h). The living room is not ventilated, once other rooms have ventilation rates above the minimum hygienic standards, and sufficient air exchanges between rooms are assumed. The house had its comfort range defined between 18˚C and 28˚C. At each time step, any temperature occurring outside that range causes mechanical heating to be turned on, and a temperature above that range causes mechanical cooling to be turned on.

Table 5 presents the simulation zones with thermal capacities due to furniture, and inner heat generation rates and inner heat generation rates.

Table 3: Physical properties of building materials [9].

Absorptivity to solar radiation

Transmissivity to solar radiation

Material

Thermal

cond

uctiv

ity

(W/m

K)

Specific he

at

(J/kgK)

Specific mass

(kg/m³)

red

green

blue

red

green

blue

Masonry 0.80 700 1000 Timber, door 0.18 1800 500 Concrete 1.0 1100 2400 Single glazing 1.0 2400 Ceramic roof tiles 0.6 700 2000 Double glazing 0.11 700 1500 0.1 0.1 0.1 0.9 0.9 0.9 Timber, ceiling 0.10 1500 550 0.1 0.9 0.8 0 0 0 Masonry (11 cm)+rock wool (5 cm)+plaster (1 cm) 0.121 641 1478 0.1 0.9 0.8 0 0 0 Concrete + rock wool (5 cm) +plaster (1 cm) 0.117 641 861 0.5 0.5 0.5 0 0 0


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Table 4: Simulation zones with ventilation rates (m³/h) [9].

Room Bedroom 1 BWC Bedroom 2 Kitchen Living room Attic 0-‐6 0.015 0.0015 0.015 0.015 0 0.1 6-‐12 0.015 0.0015 0.015 0.015 0 0.1 12-‐18 0.015 0.0015 0.015 0.015 0 0.1 18-‐24 0.015 0.0015 0.015 0.015 0 0.1

Table 5: Thermal zones: heat capacity and indoor heat energy generation rate [9].

Heat capacity (J/K) Room Bedroom 1 BWC Bedroom 2 Kitchen Living Attic

500,000 300,000 500,000 500,000 500,000 500,000

Obs. Furniture, apparel

Sanitary ware

Furniture, apparel Furniture, dishware Furniture Roof truss

Time (h) Indoor heat generation (W) 0-‐1 160 0 160 300 30 0 1-‐2 160 0 160 300 30 0 2-‐3 160 0 160 300 30 0 3-‐4 160 0 160 300 30 0 4-‐5 160 0 160 300 30 0 5-‐6 160 0 160 300 30 0 6-‐7 160 0 160 300 30 0 7-‐8 0 6,000 0 2,800 30 0 8-‐9 0 0 0 300 30 0 9-‐10 0 0 0 300 30 0 10-‐11 0 0 0 300 30 0 11-‐12 0 0 0 5,500 30 0 12-‐13 0 0 0 500 30 0 13-‐14 0 0 0 300 30 0 14-‐15 0 0 0 300 30 0 15-‐16 0 0 0 300 30 0 16-‐17 0 0 0 300 30 0 17-‐18 0 0 0 300 30 0 18-‐19 0 6,000 0 5,600 30 0 19-‐20 0 0 0 600 400 0 20-‐21 0 0 200 400 400 0 21-‐22 0 0 200 300 400 0 22-‐23 0 0 200 300 200 0 23-‐24 0 0 200 300 200 0

Table 6: Operation energy consumption and costs [9].

A B C D E

Energy consumption

Heating (kWh/year) 5,106 3,016 21,27 1,858 534

Cooling (kWh/year) -‐5,877 -‐6,368 -‐6,642 -‐6,725 -‐7,602

Heating+cooling (kWh/year) 10,984 9,384 8,769 8,583 8,136

Heating+cooling, difference (kWh/year) -‐1,600 -‐2,215 -‐2,401 -‐2,848

Heating+cooling, difference (MJ/year) -‐20,945 -‐28,996 -‐31,431 -‐37,283

Costs

Heating energy costs, (US$/year) 1,048 619 436 381 109

Cooling energy costs, (US$/year) 1,206 1,307 1,363 1,380 1,560

Heating+cooling energy costs, (US$/year) 2,254 1,925 1,799 1,761 1,669 Heating energy costs: difference ,

(US$/year) 0 -‐429 -‐611 -‐667 -‐938

Heating+cooling energy costs, difference, (US$/year)

0 -‐328 -‐454 -‐493 -‐584


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Table 7: Energy payback time calculation [9].

A B C D E

Hot & cold air conditioning

increased embodied energy (MJ) from Table 1 0 9,749 13,044 21,284 29,517

saved operation energy (MJ/year) 0 -‐20,944 -‐28,997 -‐31,424 -‐37,285

energy payback time (years)

0.46 0,44 0,67 0,79

Hot air conditioning & ventilation increased embodied energy (MJ) from Table 1 0 9,749 13,044 21,284 29,517

saved operation energy (MJ/year) 0 -‐7,524 -‐10,724 -‐11,693 -‐16,459

energy payback time (years)

1.29 1.21 1.82 1.79

Table 8: Monetary payback time calculation [9].

A B C D E

Hot & cold air conditioning

increased construction costs from Table 2 (US$) 0 2,105 2,306 5,436 7,141

Saved operation costs (US$/year) 0 -‐329 -‐455 -‐493 -‐585

monetary payback time (years)

9.04 6.61 24.26 34.17

Hot air conditioning + ventilation

increased construction costs from Table 2 (US$) 0 2,105 2,306 5,436 7,141

Saved operation costs (US$/year) 0 -‐429 -‐612 -‐667 -‐938

monetary payback time (years)

6.34 4.59 13.06 11.70

3 Results and discussion

Results and discussion on operation energy and costs are presented below.

3.1 Operation energy

Table 6 presents simulation results: operation energy consumption values and respective costs for the scenarios A to E, separated by heating and cooling situations.

The adopted electric energy tariff to the residential consumer is US$ 0.2047 (R$ 0.69118/kWh) [22], which is valid since June 24 2016. This tariff includes the value of US$0.7042 (R$0.25062) to account for the ICMS and PIS/COFINS taxes.

A reduction in heating costs is observed, mainly, in the transition from scenario A to scenario B. The increase in cooling costs is also observed, as the building envelope becomes more insulated and therefore dependent on mechanical cooling. Although the thermal insulation brings improvement in the prevention of radiant heat fluxes descending from the roof, also of vertical walls which, despite having light colours, absorb heat from direct sunshine, a liquid effect of imprisoning inner generated heat is observed.

3.2 Energy payback

Next, simple energy payback calculations are presented.

Figure 7: Progressive energy payback time of scenarios A

through E under hot and cold air conditioning [9].

Figure 8: Progressive energy payback time of scenarios A through E under hot air conditioning in winter and natural

ventilation in summer [9].


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Figure 7 presents the energy payback time of scenarios A to E, in the case that mechanical air conditioning is simply turned on the whole year.

In a wholly mechanized air conditioning one can assume that ventilation follows a theoretical model. However, if natural ventilation is used, the ventilation rates, most probably, are in disagreement with the actual conditions, once there is the influence of local wind conditions, as well as vertical temperature gradients, which are not taken into account by Mestre, as it happens with the majority of simulation systems which assume concentrated mass.

Figure 8 corresponds to the case in which a mechanical air conditioning in winter and natural ventilation in summer. Natural ventilation, as a strategy to achieve thermal comfort in summer, is sufficient in Curitiba. A simulation of scenario E, modified to consider a ten times stronger ventilation air flow, and also considering that the living room is ventilated at 0.15 m³/s, leads to an almost null energy consumption in summer.

Table 7 presents the calculation of energy payback time, which ranges from 0.45 years (scenario C) to 0.79 years (scenario E) when considering hot and cold air conditioning. These surprisingly low values are the main finding of the present paper: rock wool as an insulation material to a single family residence has a short energy payback time even in a temperate climate.

3.3 Costs

The following cost calculations were based on the compound interest formula at an annual rate of 7.5%.

Table 8 presents the calculation of monetary payback time, which ranges from 6.6 years (scenario C) to 34.2 years (scenario E) when considering hot and cold air conditioning. Figures 9 and 10 present the evolution of operation energy costs along scenarios A to E.

The retrofit scenario which has shortest payback time is C. Scenario D, substitution of single glazing windows by double glazing windows, is least attractive, as it involves a costly operation, mainly because there is not a developed market of standardized double-‐glazing products in Brazil.

Figure 9: Costs considering mechanical heating and cooling [9].

Figure 10: Costs considering only mechanical heating [9].

Only scenarios B and C have proved an attractive investment, although not at a comparable rate to the energy payback. The arrow gradient at Figures 9 and 10 suggests that the addition of rock wool under the floor slab is slightly less profitable than B scenario and therefore should be made prior to the glazing replacement, which has not proved a profitable operation in the present case.

4 Conclusion

The energy retrofit of a social housing unit located in Curitiba using the addition of rock wool to envelope walls and, further, of other insulation items was analysed as to its energy and monetary payback time. Conclusions may not be generalized for other locations in Brazil due to climate and transportation distances.

If the energy payback is considered, the retrofit actions considered in scenarios B through E make sense; in terms of investment, only for rock wool (not for double glazing), and at a much lower rate than in terms of energy.

As the analysis was conducted in a temperate climate, the effects are felt in both cases (cooling and heating loads). A similar analysis conducted in climates which are only cold or only hot would show more extreme situations, leading to much shorter payback times. It is relevant to consider that the “passive operation of the house requires an active occupant”.1

The analysis makes evident that the energy costs are comparatively high to the residential consumer, and low to the industry, and suggests the presence of heavy subsidies of energy costs to industry. Under such circumstances, a comprehensive energy efficiency programme will divide opinions.

A public policy aiming at energy efficiency should consider the liquid result of building retrofits, as well as the whole industry chain. It is necessary to consider energy in the pre-‐operation phase.

Acknowledgements

Authors are indebted with Mr. Fábio Motta (Rock Fibras) for the hospitality and information provided.

1 -‐ A motto by Prof. Dr.-‐Ing. Jürgen Schmid (1944-‐2013), an European pioneer in the technology of renewable energy and doctoral advisor to the first author.


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References

[1] M. S. AL-‐HOMOUD, "Performance characteristics and practical applications of common building thermal insulation materials.," no. 40, pp. 353-‐366, May 2004.

[2] A. P. MELO and R. LAMBERTS, "Envelope insulation and heat balance in commercial buildings.," in Eleventh International ibpsa, 2009.

[3] EIA, "Residential Energy Consumption Survey (RECS)," EIA, Washington, 2011.

[4] EIA, "Energy consumption expenditures, and emissions indicators, 1949-‐2004," 2006.

[5] B. UPTON, R. MINER, M. SPINNEY and L. S. HEATH, "The greenhouse gas and energy impacts of using wood instead of alternatives in residential construction in the United States.," Biomass and Bioenergy, vol. 32, no. 1, 2008.

[6] A. BOLATTÜRK, "Determination of optimum insulation thickness for building walls with respect to various fuels and climate zones in Turkey.," Applied Thermal, no. 43, pp. 1055-‐64, 2006.

[7] W. INSTITUTE, "Final Report on the Material Efficiency and Resource Conservation (MaRess) Project," 2010.

[8] M. G. R. S. R. A. PFUNDSTEIN, "Dämmstoffe: Grundlagen, Materialien, Anwendungen. Detail Praxis.," Detail, Munich, 2007.

[9] R. C. M. M. HABIB, "Tempo de Retorno Energético de Isolantes Térmicos na Climatização de Edificações: Estudo de Caso da Lã de Rocha à Zona Bioclimática 1 do Brasil.," Masters, Thesis, (2014).

[10] M. LEONARDI, "Price information of products by Isar -‐ Isolamentos Térmicos e Acústicos," Jan 2017.

[11] P. J. F. A. U. MENDONÇA, "Habitar Sob Uma Segunda Pele," Doctoral, Thesis, 2005.

[12] F. MOTTA, "Personal communication," 2013.

[13] R. A. SILVA, "Price information of products by CELPROM," 25 Fev 2017.

[14] IBGE, "cidades.ibge.gov.br," 2017. [Online]. Available: http://cidades.ibge.gov.br/xtras/perfil.php?codmun=410690. [Accessed Jan 2017].

[15] P. AMERICAS, "Life Cycle Assessment of Mineral Wool Insulation Products," Colorado -‐ US, 2010.

[16] GRODAN, " Rockwool as a Growing Substrate for Hydroponic Systems," . Roerdmond -‐ The Netherlands 2004. Available under < http://grodan101.com/knowledge-‐center/rockwool-‐growing-‐substrate-‐hydroponic-‐systems, 2004. [Online]. Available: http://grodan101.com/knowledge-‐center/rockwool-‐growing-‐substrate-‐hydroponic-‐systems. [Accessed 2014].

[17] I. f. I. B. IFIB, "Baustoffdaten – Ökoinventare," Technische Hochschule (ETH) Zürich; M. Holliger, Holliger Energie Bern, Karlsruhe / Weimar / Zürich, 1995.

[18] S. F. TAVARES, "Metodologia de Análise do Ciclo de Vida Energético de Edificações Residenciais Brasileiras," Doctoral thesis, 2006.

[19] A. B. D. N. T. (ABNT), "NBR 12721: Avaliação de custos unitários e preparo de orçamento de construção para incorporação de edifícios em condomínio – Procedimento.," ABNT: Associação Brasleira de Normas Técnicas, Rio de Janeiro, 2006.

[20] UOL, "economia.uol.com.br/cotacoes /cambio/ dolar-‐turismo-‐estados-‐unidos/?historico," 2017]. [Online]. Available: https://economia.uol.com.br/cotacoes /cambio/ dolar-‐turismo-‐estados-‐unidos/?historico. [Acesse on Jan. 2017].. [Accessed Jan 2017].

[21] A. L. SCHMID and H. F. GRAF, "Validation of MESTRE Building Simulation System according to Best-‐Test Multi-‐Zone, Non-‐Airflow, In-‐Depth Diagnostic Cases," in Proceedings of Building Simulation 2011: 12th Conference of International Building Performance Simulation Association, Sydney -‐ Australia, 2011 -‐ , In-‐Depth Diagnostic Cases. In Proceedings of Building Simulat.

[22] http://www.copel.com/hpcopel/root/nivel2.jsp?endereco=%2Fhpcopel%2Froot%2Fpagcopel2.nsf%2F5d546c6fdeabc9a1032571000064b22e%2Fe3a5cb971ca23bf503257488005939ba. [Accessed Jun 2017]

ISSUE27!!|!!October!!2017 · 2017. 11. 6. · !!!!!ESPAÇO!ENERGIA!!| !!!ISSUE27!!|!!October!!2017...

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