energy consumption and co2 emission reduction for space heating using...

46th Annual Conference of the Architectural Science Association (ANZAScA), 2011, Griffith University

Energy Consumption and CO2 Emission Reduction for Space Heating using SAP in Chilean Dwellings

Angeles Hevia

University College London (UCL), London, United Kingdom ABSTRACT: Fifty two percent of the energy consumption in Chilean dwellings comes from space heating. The country depends by an 80% on fuel imports. An increase in energy prices and fuel supply problems have obligated Chile to consider cheaper forms of energy such as wood, affecting people's health. The aim of this study is to reduce energy consumption and CO2 emissions caused by space heating implementing the UK's SAP methodology in Chilean dwellings. The measures consisted of increasing the airtightness, reducing the thermal bridging and implementing energy efficient building services. Based on the current Chilean Thermal Regulations, walls were improved by making their u-values more even compared to the ones in roof and floor. Zones 1 and 2 reduced energy up to 75% with savings in CO2 emissions up to 21%, by adding external insulation, reducing thermal bridging and air permeability. In the case of zones 4 to 7, the maximum energy savings were up to 71% considering CO2 emission reductions of 48%. These were achieved by implementing thermal envelope improvements and solar collectors. Zone 3 was recommended to improve the fabrics in complement to using electric wall panel heaters reducing energy by 43% and CO2 emissions by 75%. Conference theme: Buildings and energy Keywords: Energy, Space-Heating, SAP, Chile

1.0. INTRODUCTION

Chile has a lack in natural gas resources, depending on imports since 1997 (CEI UC, 2009). In 2004, the natural gas exportation from Argentina was restricted halving the supply during some periods (CEI UC, 2009). The capacity of oil production in Chile is only 6.3% of its total real demand, which increases the reliance on foreign imports (CEI UC, 2009). Fifty two percent of the energy consumption in Chilean dwellings comes from space heating (CNE cited in Armijo, 2009). Although wood is the cheapest fuel its combustion is not an environmentally friendly solution because it causes deforestation and reduces absorption of carbon dioxide (CO2) by tress, increasing health and inequity problems. Burning wood in Chile is a dramatic issue. Being the cheapest fuel, it provides space heating to almost half of the houses. Carbon dioxide emissions in Chile increased by 79% from 1990 to 2008 (IEA, 2008)

The Chilean Thermal Regulation has set no target values for thermal bridging or air permeability. It hasn't either considered the efficiency of the heating systems. Neither are considered the free gains such as solar or internal gains or an external base temperature to set the artificial heating. Regulations consider thermal resistance values in walls that are quite distant compared to the ones in roof and floor producing heat losses in the areas with less resistance. This increases the risk of cold spots (Burgos, 2011). No recommended ventilation rates or target humidity levels have been set, such as the ones stated by the UK's CIBSE, which recommends a minimum of 0.4 air changes per hour (ACH) for dwellings and humidity levels between 40% and 70% in order to avoid mould growth. Carbon dioxide emissions are still not considered when applying for a building license in Chile.

Notwithstanding, the Standard Assessment Procedure (SAP) is a methodology adopted by the UK Government in order to assess the energy performance of dwellings. It considers energy consumption as well as dwelling emission rate (DER) calculations measured due to space and water heating, ventilation and lighting, deducting the emissions saved by renewable technologies. Thermal bridging and air permeability heat losses are also considered.

1.1. Aims and Objectives

The aim of this study is to reduce energy consumption and CO2 emission caused by space heating in Chilean dwellings using the SAP methodology. The objectives are:

- Reduce heat loss produced by the thermal envelope by making u-values comparable - Provide energy efficient solutions by reducing thermal bridging and increasing airtightness but still achieving appropriate ventilation rates - Calculate the energy consumption and CO2 emission that could be saved by improving efficient measures for space heating - Include free heat gains and heating degree-day calculations for reducing energy and CO2 emission


- Verify if the energy subsidy for solar collectors is a proper solution for reducing space heating

2.0. METHODOLOGY

The 2005 SAP methodology, implemented in the UK, is used to measure the energy consumption and CO2 emission in Chilean dwellings throughout the seven thermal zones. The study is divided in six simulations with dwelling typologies based in the 2002 Chilean Population Census (CChC, 2010) (Figure 1). Thermal zones 1, 2, 6 and 7 used typology 1, whereas thermal zones 3, 4 and 5 used dwelling typology 5. In order to adapt the 2005 SAP version to the Chilean thermal zones, seven weather files had to be found. Carbon Dioxide emission factors for fuels used in Chilean dwelling´s heating systems were obtained from the International Energy Agency (IEA, 2008). The energy consumption was measured in kWh/year whereas the CO2 emitted by the dwellings in this Initial Case represents the Target Emission Rate (TER). Later on, a Dwelling Emission Rate (DER) considers the CO2 emission after the dwellings were improved. They are both measured in kgCO2/m2/year.

Source: (CChC) Figure 1: Dwelling typologies 1 and 5

2.1. First Simulation: Initial Case The first simulation is based in an Initial Case, which considers a dwelling in compliance with the Second Stage of the Chilean Thermal Regulation, regarding thermal transmittance values for roof, floor, walls and windows (Table 1). Since the Chilean Thermal Regulation has not set target values for heat losses caused by thermal bridging, a value of 0.15 W/mK, was assumed (BRE, 2005). An air leakage rate of 15 m3/hm2@50Pa was considered since the pressurisation test result has been avoided as not required by the current regulations (Building Regulations, 2010). The space heating and ventilation systems used are based in the 2002 Census (CChC, 2010).

Table 1: Summary Table for Initial Case

U-values Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 Wall thickness 71 mm. 71 mm. 71 mm. 71 mm. 71 mm. 71 mm. 71 mm. Required Wool Fibre

no no 30 mm 30 mm 30 mm 30 mm 50 mm

Wall (W/m2K) 4.0 3.0 1.9 1.7 1.6 1.1 0.6 Floor (W/m2K) 3.60 0.87 0.70 0.60 0.50 0.39 0.32 Roof (W/m2K) 0.84 0.60 0.47 0.38 0.33 0.28 0.25 Windows (W/m2K) 5.70 5.70 5.70 5.70 5.70 3.60 3.60 Thermal Bridging (W/mK) 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Air permeability (m3/hm2@50Pa) 15 15 15 15 15 15 15 Ventilation rate ACH 0.79 0.79 0.79 0.79 0.79 0.79 0.79 Ventilation system System Natural Natural Natural Natural Natural Natural Natural Category Low Low Low Low Low Low Low Space Heating System (device) Electric LPG LPG Wood Wood Wood Wood

2.2. Second Simulation: Thermal Bridging and Airtightness The second simulation, as well as the other five, uses the same u-values and space heating systems as the ones used in the Initial Case. Since the Chilean Thermal Regulation does not consider target values for thermal bridging or airtightness, this study has been based on the UK's standards such as the Accredited Construction Details, The Government’s Standard Assessment Procedure for Energy Rating of Dwellings and the Building Regulations Part L1A 2010. Accordingly, the value for thermal bridging was 0.8 W/mK and the air permeability 7 m3/hm2@50Pa. These values were accomplished as a consequence of using draught proofing in doors and windows, implementing insulation continuity, simple designs with minimum construction types and controlling the air barrier line reducing the air passage between interior and exterior (DCLG, 2007, p.5).


2.3. Third Simulation: Building Services A third simulation was made to improve the building services of the Initial Case. These were improved by changing the system, the efficiency or both.

Table 2: Proposed Building Services

Space Heating Initial System Electric LPG LPG Wood Wood Wood Wood Efficiency 100% 80% 80% 65% 65% 65% 65% Condensing boiler Efficiency N/A 90% 90% 90% 90% 90% 90% Wood Efficiency N/A N/A N/A 75% 75% 75% 75% Electric Wall panels Efficiency N/A 100% 100% 100% 100% 100% 100% Air Heat pump Efficiency 250% 250% 250% 250% 250% 250% 250%

2.4. Fourth Simulation: Renewable Energy The chosen renewable energy system was solar, considering that the Chilean government has a subsidy for implementing solar collectors in dwellings. Flat panels were proposed, with 78% efficiency, orientated towards the north and with an angle of inclination calculated by adding 10º to the latitude of the site where located (The Green Building Bible V2, 2008). 2.5. Fifth Simulation: Wall Improvements The Chilean Thermal Regulation has distant target thermal transmittance values between roof, walls and floor, with higher heat losses in the areas with higher u-values, such as thermal zones 1 and 5 where wall u-values are five times larger than the ones in the roof. Insulation is added to the brick walls externally, allowing the thermal mass to store the heat during the day releasing it to the inside when the external temperatures decrease at night.

Table 3: Proposed wall improvements

Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 Initial u-values Wall u-value (W/m2K) 4.0 3.0 1.9 1.7 1.6 1.1 0.6 Floor u-value (W/m2K) 3.60 0.87 0.70 0.60 0.50 0.39 0.32 Roof u-value (W/m2K) 0.84 0.60 0.47 0.38 0.33 0.28 0.25 Proposed Walls External insulation (mm) 10 10 40 50 50 80 100 Insulation type EPS Wool Fibre Wool Fibre Wool Fibre Wool Fibre Wool Fibre EPS Wall u-value (W/m2K) 1.86 1.19 0.63 0.54 0.54 0.39 0.32

3.0. RESULTS AND ANALYSIS Energy consumption and CO2 emission reductions achieved by the proposed measures are presented as follows. A detailed analysis of the impact these measures had in each thermal zone is detailed in the Results Analysis.

3.1. Result 1: Thermal Bridging and Airtightness improvements Reducing thermal bridging and air permeability decreased energy consumption in zones 4 and 7 by almost 18% whereas zone 2 lessened it by 10.9% (Figure 2).

Figure 2: Energy efficient measures implementing Thermal Bridging and Air permeability

Zones 1, 5 and 6 presented energy reductions of 16% whereas zone 3 by 13.2%. For CO2 emissions, reductions increased towards the south ranging from 3.1% to 13.2%. Although the airtightness increased, ventilation rates were still appropriate with 0.59 ACH. However, it is assumed that the occupant will open the windows or that vents were implemented to keep proper ventilation rates.


3.2. Result 2: Building Services improvements MVHR The use of MVHR did not have major reductions either in energy consumption or CO2 emissions (Figure 3). The maximum decrease was observed in thermal zone 4 with 1.5%. Zone 5 had a positive result in CO2 savings with 4% reduction.

Figure 3: Energy efficient measures implementing MVHR (left) and Condensing boiler (right)

Condensing Gas boiler This measure allowed thermal zone 1 to reduce energy consumption by 59.3% (Figure 3). Zones 5 to 7 achieved reductions of 35%. The DER increased by 44.6% over the TER in thermal zone 1, whereas in zones 2 and 3 it reduced by 45.5%. Wood Stove The wood stove measure was applied in zones 4 to 7 with an average energy reduction of 13% whereas CO2 emission, achieved the highest reduction of 19.3% in thermal zone 4 (Figure 4).

Figure 4: Energy efficient measures implementing Wood Stoves (left) and Electric Resistance Heat (right)

Electric Wall Panel Heaters Thermal zones 4 to 7 reduced energy consumption by 40%. The lowest results were observed in thermal zones 2 and 3 with reductions of 3.1% and 17.2% respectively (Figure 4). The DER was reduced by almost 60% in zones 2 and 3, whereas zones 4 to 7 achieved reductions of almost 40%. Heat Pumps Heat pumps demonstrated the maximum energy reduction of 72% in zones 4 to 7. In northern locations, a maximum reduction of 61.4% was observed in thermal zone 3. Carbon dioxide emission presented an important decrease throughout thermal zones 2 to 7 with a DER reduced by over 50%. The maximum reduction was observed in zone 3 with 71.6%, whereas the minimum was detected in thermal zone 1 with 5.7% 3.3. Result 3: Renewable Energy Solar Collectors

Figure 5: Energy efficient measures implementing Solar Collectors (left) and Wall Improvements (right)


Solar collectors reduced energy by 52.9% in thermal zone 1 (Figure 5). Energy savings decreased towards the south. However, zones 2 and 3 increased their energy consumption by 2.5% and 13.9% respectively. Zone 2 achieved CO2 emission reductions of 51.2%. Zones 4 to 7 lessened CO2 emissions ranging from 25.1% to 11.8%. However the DER increased over the TER by 8.4% in zone 1.

3.4. Result 4: Wall Improvements Increasing the resistance in walls had positive results throughout all zones. The measure had the largest impact in thermal zone 1, reducing energy consumption by 60.1% (Figure 5). Thirty eight percent reduction was observed in zone 2 followed by zone 6 with savings of almost 30%. The lowest rates were observed in zones 3, 4, 5 and 7 ranging from 12% to 15%. The DER was reduced by almost 20% compared to the TER in thermal zone 6 followed by zone 2 with emissions reduced by 16%. Zone 1 and 7 had CO2 emission reductions of 11.5% and 9.9% respectively whereas the lowest savings were observed in thermal zones 3 to 5 with an average of 7%.

3.5. Analysis of Results The final measures were chosen considering energy savings, CO2 emission reductions and capital costs. The CO2 reductions were subordinated to energy consumption that managed to achieve savings of almost 50%, since dwellings with energy reductions up to 60% are currently being constructed as they are attractive to the market.

3.5.1. Thermal Zone 1 The best results for energy consumption were observed when implementing a condensing gas boiler and reducing the u-values of the walls, saving almost 60% (Figure 6). Solar collectors reduced energy consumption as well as air source heat pumps by 52.9% and 40% respectively. Reducing the thermal bridging ratio and increasing the airtightness, reduced energy consumption by 15.5%.

Figure 6: Energy and CO2 savings for thermal zone 1

Energy savings between adding insulation and implementing a condensing boiler are quite similar, however, the former considers costs £33 whereas the latter £638. Similarly, air heat pumps have a high coefficient of performance (CoP), but their capital cost is too expensive. Accordingly a better option would be adding draught proofing in windows. Therefore, the most suitable measures are reducing thermal bridging, increasing airtightness and externally insulating the walls. The improved dwelling consumes 141 kWh/year for space heating and emits 19.3 kgCO2/m2/year.

3.5.2. Thermal Zone 2

The Initial Case for thermal zone 2 consumes 2,711 kWh/year and releases 95.1 kgCO2/m2/year (Figure 7). Implementing a condensing gas boiler diminished CO2 emissions by 45.4%. The same savings were achieved by reducing thermal bridging and increasing the airtightness.


Although electric wall panel heaters reduced CO2 emission by 60.4% fuel usage was only lessened by 3.2%. The measures with the highest energy savings were air heat pumps and wall improvements saving annually 51.8% and 45.4% respectively (Figure 7). Although the latter reduced CO2 emissions by only 16.1% compared to 59.1% lessened by the former, capital costs are lower when insulating the walls. When insulation was complemented to draught proofing in doors and windows, CO2 emission diminished by 21.1% with annual energy savings of 56.4%. For


thermal zone 2 the most suitable option is to externally insulate walls with 10 mm wool fibre as well as doors and windows with draught proofing. The improved dwelling consumes 1,181 kWh/year emitting 75 kgCO2/m2/year.

3.5.3. Thermal zone 3

The Initial thermal zone 3 consumes 3,847 kWh/year and releases 96 kgCO2/m2/year. Air source heat pumps, allowed not only savings of 61.4% but also reduced CO2 emissions by 71.7% (Figure 8). However, reducing air permeability, lessening thermal bridging ratios, adding external insulation and using electric wall panel heaters reduced altogether energy consumption by 42.9% and CO2 emissions by 74.7%. The best options for zone 3 include adding draught proofing in windows and doors, adding 40 mm wool fibre insulation to walls with electric wall panel heaters. The improved dwelling showed an energy consumption of 2,196 kWh/year emitting 24.2 kgCO2/m2/year of carbon dioxide.




The Initial Case for thermal zone 4 consumes 4,249 kWh/year and releases 55.2 kgCO2/m2/year. Fabric improvements decreased energy by 33% reducing CO2 emissions by 15.2%. Electric wall panel heaters and air source heat pumps, permitted energy savings of 41.5% and 72.1% respectively (Figure 9). The former reduced CO2 emissions by 42.2% whereas the latter achieved a reduction of 54.5%. Condensing gas boilers achieved energy savings of 38.8% with CO2 reductions of almost 16%. Heat pumps reduced energy by 72.1% and CO2 by 54.5%. Nonetheless fabric improvements with solar collectors, saved energy up to 62.4% and CO2 reductions of 40.4% with and initial cost of £114 much lower than condensing boilers or electric systems. The improved dwelling for thermal zone 4 consumes 1,598 kWh/year and releases 32.8 kgCO2/m2/year.



The Initial Case for thermal zone 5 consumes 8,280 kWh/year and releases 79 kgCO2/m2/year (Figure 10). Solar collectors saved 25.5% in running costs diminishing CO2 emissions by 18.5%. Improving the thermal envelope with draught proofing and external insulation in walls reduced energy usage by almost 28% reducing CO2 emissions by 17.2%. Nonetheless, they achieved better results compared to solar collectors and are the cheapest measure


compared to electric or gas fuelled systems with a capital cost of £179. Wall panel heaters and air heat pumps had annual energy savings of 40.7% and 72.6% respectively. Carbon dioxide emissions were reduced by 40.8% and 58.6% respectively. Implementing a condensing gas boiler achieved energy savings of 35.4% lessening CO2 emissions by almost 16%.

Although air source heat pumps demonstrated better results compared to a condensing gas boiler, the latter has a lower cost of £638. Nonetheless, implementing a condensing gas boiler in complement to 50 mm wool fibre insulation and draught proofing, reduced energy by 63.4% and CO2 emissions by 33%. Insulating walls, adding draught proofing and implementing solar collectors saved energy by 53.4% and CO2 by 35.7%. However, fabric improvements installed with solar collectors has a capital cost of £179, whereas fabric improvements installed with a condensing boiler has a capital cost of £817 (Table 10). For these reasons, the best solution is to improve walls, add draught proofing and implement solar collectors saving 53.4% of energy and CO2 emission reduction of 35.7%. The improved dwelling has an energy consumption of 3,855 kWh/year releasing 50.7 kgCO2/m2/year.


The Initial Case for thermal zone 6 consumes 9,502 kWh/year and releases 101.3 kgCO2/m2/year (Figure 11). Although CO2 emissions were reduced by only 16% when implementing a condensing gas boiler, energy decreased by 35.3% (Table 11). Complementing this system with draught proofing as well as externally insulating walls with 80 mm wool fibre reduced energy by 81% and CO2 by 46.7%. Although heat pumps achieved better results, a gas-fuelled system is cheaper.


Insulating walls and adding draught proofing achieved energy savings of 45.7% reducing CO2 emissions by 30.5%. On the other hand, although implementing a condensing gas boiler with an improved fabric allowed larger reductions in energy and CO2 emissions, solar collectors in complement to an airtight well-insulated building accomplished similar savings. These measures allowed not only to take advantage of the government's subsidy but also to achieve energy savings of 71%, lessening CO2 emissions by 47.4%. The improved dwelling has an energy consumption of £2,754 kWh/year releasing 53.2 kgCO2/m2/year.


The Initial Case for thermal zone 7 consumes 15,460 kWh/year and releases 142.6 kgCO2/m2/year. Fabric improvements achieved annual energy savings of 30.4% decreasing CO2 emission by 23.4% (Figure 12). Solar collectors achieved energy savings of 21.5% diminishing CO2 by almost 12%, and when combined with fabric improvements it achieved energy savings of 51.9% and CO2 emission reductions of 35.3%. The condensing gas boiler achieved cost savings of 32% although CO2 emissions decreased by only 14.2%. Combining this option with increasing wall insulation and draught proofing it reduced energy by 62.4% lessening CO2 emissions by 37.5%.

Implementing electric wall panel heaters or air heat pumps are attractive solutions with energy reductions of around 70%. However, implementing 100 mm of expanded polystyrene in walls, reducing thermal bridging and air permeability and installing solar collectors has a cost of £520 reducing energy by 51.9% with CO2 emission savings of 35.3%. The improved dwelling consumes 7,433 kWh/year and releases 92.2 kgCO2/m2/year.



4.0. CONCLUSION

Increasing wall insulation thickness enabled achieving maximum energy reductions of 60% (zone 1) with maximum CO2 emission reductions of 20% (zone 6), demonstrating what stated in the Literature Review: resembling the importance of proposing even u-values for achieving a heat loss reduction (Burgos, 2010). Reducing thermal bridging and air permeability achieved the highest energy reductions in zones 4 and 7 with 18% whereas zone 7 reduced CO2 emission by almost 13%. Ventilation rates obtained in SAP when increasing airtightness (0.59 ACH) demonstrated to comply with minimum requirements (0.4 ACH). However these results considered the occupant behaviour hindering to conclude which are the real effects of airtightness in ventilation. The fabric measures stated above enabled altogether a maximum energy reduction of 75% in zone 1 whereas the minimum was observed in zone 3 with 25% reduction. The maximum CO2 emission was reduced by 30% in zone 6 whereas the minimum was in zone 3 by 12% (Table 31). This allows us to conclude that fabric improvements are an appropriate solution when intending to reduce energy consumption and CO2 emissions.

The aim of this study was to reduce energy consumption and CO2 emission caused by space heating in Chilean dwellings throughout the SAP methodology. It was fulfilled because the proposed measures achieved reductions in energy consumption over 50% in most of the zones with CO2 emission reductions up to 75%.

Since zones 1 and 2 have low heating requirements, thermal envelope improvements are suggested, achieving energy reductions of 76% and 56% respectively. Carbon dioxide emission was reduced by 15% in the former whereas the latter diminished by 21%. The suggested measure for zone 3 considers improving the thermal envelope and implementing electric wall resistance enabling savings of 75% in CO2 emissions. Although this zone presented the lowest results for energy savings (43%) fabric improvements could still be considered to achieve better results by increasing the insulation thickness. Thermal envelope improvements in complement to solar collectors were the most appropriate solution for zones 4 to 7 with maximum energy and CO2 emission reductions of 71% and 48% respectively.

As far as the author is concerned, the Chilean Government does not support measures such as implementing insulation in dwellings. However, these should be taken into account for reducing space heating requirements considering a future subsidy for implementing these, before investing in more expensive technologies such as renewable energies. Sustainable architecture starts from implementing low cost and simple measures such as adding insulation, reducing thermal bridging and increasing airtightness.

REFERENCES

Armijo, G. (2009) Impact of an Energy Refurbishment Programme in Chile: More than Energy Savings. Earthscan: London, UK

BRE, (2005) The Government's Standard Assessment Procedure for Energy Rating of Dwelings. BRE: Watford

Building Regulations (2010) Approved Document L1A. NBS: London

Burgos, D. (2011) Thermal Regulations: Just the First Step. Retrieved from: http://www.revistatc.com/?p=3898

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Hevia, A. (2011) Energy Consumption and CO2 Emission Reduction for Space Heating using SAP in Chilean Dwellinsg (Dissertation for MSc Environmental Design and Engineering UCL) Unpublished

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Treasury Department of Chile (2009) Subsidy for Solar Thermal Systems. Treasury Department: Santiago, Chile

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