Performance Assessment of Earth Constructions ... - Science Direct

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ScienceDirect Procedia Engineering 180 (2017) 502 – 509

International High- Performance Built Environment Conference – A Sustainable Built Environment Conference 2016 Series (SBE16), iHBE 2016

Performance assessment of earth constructions under the Chilean energy rating system software María José Morenoa*, Francesco Fioritob b

a The University of Sydney, Faculty of Architecture, Design and Planning, 148 City Rd, Darlington NSW, Sydney 2006, Australia The University of New South Wales, Faculty of Built Environment, Red Centre West Wing, Kensington NSW, Sydney 2052 ,Australia

Abstract This research aims to evaluate the benefits of energy savings in earth constructions, in the Chilean climatic context. Another aim is to identify how well CCTE_CL v2.0 software (CCTE), used by the Chilean energy rating system, is able to predict energy consumption in earth constructions. Understanding the parameters, assumptions and limitations utilized by the software and how they affect the evaluation is also within the aims. A case study with exterior earth walls was created and compared with a second model with a lightweight construction system. Both exterior walls have the same U-value; therefore, its difference remains only in the mass of the exterior walls. The models were built in CCTE software and then replicated in a more advance software, in this case Design Builder. This allowed for comparing their performance. It was found that the use of earth walls is able to generate a reduction in energy demand when compared to a lightweight construction system. Another finding is that, although CCTE software is able to address the incorporation of earthen materials and predict the benefits of thermal mass, some parameters embedded in the software can lead to an underestimation of the benefits of an earthen house. The previous, when results are compared to an evaluation performed with parameters considered by more advanced and complex software tools. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2017 The Authors.Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee iHBE 2016. Peer-review under responsibility of the organizing committee iHBE 2016 Keywords: Earth construction; thermal mass; rating tools; simulation software

* Corresponding author. Tel.: +56-99-8852702. E-mail address:[email protected]

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee iHBE 2016

doi:10.1016/j.proeng.2017.04.209

María José Moreno and Francesco Fiorito / Procedia Engineering 180 (2017) 502 – 509

1. Introduction Earth has been used as a construction material since more than 9000 years ago and examples can be found all around the world[1].It has also been estimated that from one third to one half of the world’s population lives in earth houses[2]. Nevertheless, nowadays modern earth buildings need to fulfil more requirements than their previous counterparts, like thermal regulation codes and requisites related to energy consumption and comfort. In order to check compliance with these new requirements, different tools have been developed. Sustainable rating systems, certifications and software products are among them. The previous has brought with it a concern because some regulation codes, their rating tools and the software on which they rely for the assessment procedure, do not provide results that coincide with the actual performance of earthen houses. Discrepancies have been attributed, among other factors, to the fact that codes and computer modelling tools are based completely on the steady-state thermal resistance of materials where only the U-value is relevant [3]. This is without considering that the greatest advantages of earthen materials are within its dynamic and hygrothermal behaviour, as a result of the simultaneous absorption, storage and release of both heat and moisture [4]. Several studies have evaluated the impacts of thermal mass on energy consumption and/or comfort [5; 6; 7; 8; 9; 10; 11]. Results vary widely among them considering the studies have been conducted in a wide range of climates. Two of them found that the use of massive walls, versus lightweight constructions, reduces heating energy consumption but increases, slightly, the cooling energy loads [7; 9]. Zhu, et al. [9] also concluded, after two years of monitoring two built houses, that the interior surface temperature of massive walls remains more stable than the interior surface temperature of a wood frame system. This leads to a more stable and comfortable indoor temperature in the massive-wall house. It was also confirmed that the mass walls have the ability of time lagging the transmission of heat. Kosny, et al. [6] after simulations for 10 U.S climates with a residential building with massive materials on external walls versus a lightweight system, concluded that in a wide range of U.S climates, heating and cooling energy requirements can be reduced when wood-frame systems are replaced with massive walls of an equivalent Rvalue. Currently some standards and thermal code regulations have recognized the benefits of the use of thermal mass in some climates by allowing less insulation levels, or a specific U-value increase, for buildings that incorporate thermal mass in comparison with lightweight construction systems like metal or wood-frames. ASHRAE standard 90.1 2010 for example, for its prescriptive method, admits around a 30% increase in U-values when thermal mass is used for exterior walls [10]. Earth also has a humidity buffer capacity which is its potential to stabilise indoor relative humidity fluctuations. This means it is able to absorb, store and release water vapour. Several studies related with hygrothermal properties of earth construction technologies have been carried out [12; 13]. They studied the effects, on indoor relative humidity values, of the use of stabilised rammed earth and clay composite as internal coating. In both cases the relative humidity fluctuations were reduced. Related to the Chilean context, in 2013, an energy rating system for housing was launched. It is expected to provide information and to influence the decision making process when buying a new dwelling. Although it is at a pilot stage, the plan is to make it mandatory. The rating system includes CCTE_CL v2.0 (CCTE) software as an alternative method to calculate energy demand and check compliance with the thermal regulation. The Chilean thermal regulation requires that the envelope of every residential building comply with a maximum thermal transmittance threshold. When CCTE software calculates the monthly and annual building energy consumption, it compares the energy demand with the demand of a reference building, assumed to have same geometry, characteristics and usage profiles of the initial one, but thermal transmittance values for the building envelope’s components equivalent to the maximum ones allowed for the specific climatic zone [14]. Therefore, its main objective is to be a compliance check tool. This study aims to evaluate the performance of an earthen house versus a lightweight system and understand its impact on energy savings in the Chilean climatic context. Also it aims to identify how well CCTE software is able to predict energy consumption in the case of earth constructions and understand the parameters, assumptions and limitations utilized by the software and how they could affect the energy rating of earth construction technologies.

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2. Methodology A case study was created as the means to evaluate the performance of earth constructions in residential buildings. It corresponds to a one-floor, single family house located in Pudahuel, Santiago, Chile (33º27`00 S; 70º40`00 W). The location has a Mediterranean or temperate-warm climate with dry and warm summers and winter rains (Csb) according to the Köppen climate classification [15]. It presents a diurnal temperature oscillation that can reach 17ºC during summer and 11ºC during winter [16]. Figure 1 shows the layout of the case study. The distribution is assumed from the energy efficiency guide for low-income housing in Chile [16]. It has to be noted that the design solution here presented is not meant to be representative of best practices of passive design, but it developed with the aim of carrying out a sensitive analysis of different parameters affecting thermal comfort in Chilean standard low-income houses. Two models were created in CCTE, one with a lightweight construction system (LW) on the exterior walls and another one with exterior earth walls (EW). This allowed for the evaluation of the performance of the earthen house in reference to the lightweight house performance. The LW house had a wood panel with insulation with a U-value of 1.37 W/m2K. For the EW house, an earth wall with a 50 cm thickness and a U-value of 1.38 W/m2K was created. As noted, both walls had the same U-value; therefore, they differed only in their mass. All other parameters stayed the same between the two models. Then, the two models were built in a second software, Design Builder, in order to compare the earthen house performance in each software. To be able to compare the results, the main parameters and assumptions considered by CCTE software were benchmarked in the Design Builder models. First, all the more explicit parameters considered by CCTE software were included in the Design Builder models. The parameters and their values were extracted from three sources: the software itself, CCTE v2.0 Manual del Usuario [14] and the Manual de Referencias Técnicas: Fundamentos Técnicos [17]. In relation to internal loads, sensible and latent gains and lighting and equipment loads, CCTE utilizes fixed values. These loads were addressed through occupancy schedules in the Design Builder models. The original weather file from the CCTE database was converted and loaded into the Design Builder model. Concerning the Heating Ventilation and Air Conditioning (HVAC) system operation, according to the CCTE documentation [17], the heating season is defined for each location and it only considers the months with more than 50 degree-day, over a 15 ºC base. The degree-days were calculated for the specific weather file and the resulting months were set for heating and cooling. After the previous, the annual gains and losses of each earth model (CCTE and Design Builder) were compared and the parameters associated with each heat flow, into and out of the building, were modified in the Design Builder model in order to benchmark CCTE results. This was called Calibration Process and it generated a Calibrated Model (CM-1).The parameters modified were the ground floor temperatures, infiltration rate, internal gains, surface properties and glazing properties. Also, the default Design Builder surface convection algorithms (TARP and DOE2) where replaced by the CIBSE algorithms in order to benchmark CCTE. This process also allowed for the understanding of the parameters utilized by CCTE and how they affect the assessment of earth construction technologies.

Fig. 1.Case study architectural plant


Finally, two parameters that are usually considered by the second software tool were incorporated into the CM-1, resulting in a more complex model or Extended Model (EM-1). The first one is the use of a different weather file for the location, in this case a typical meteorological year (TMY) weather file, and the second is the use of a more advanced calculation method for surface convection. Table 1 shows the models and the main parameters included or modified in each model. Table 1. Description of the main parameters included and/or modified in each model Model Name

CCTE-1

BM-1

DB -6

DB -7

DB- 8

DB-9

DB-10

DB-11 CM-1

CM-2 CM-3 EM-1

Parameter CALIBRATION PROCESS REFERENCE MODEL Geometry, orientation, location, construction materials, space type. Weather file by default: Pudahuel.bin BASE MODEL Geometry; orientation; ground temperatures; construction materials; airtightness; window frame absorbtance; emissivity; heating ON only from April to September, cooling ON only from October to March, HVAC set points, COP values; occupancy; internal loads; weather file, Pudahuel.epw converted from Pudahuel.bin. Ground floor exchange BM-1 + Ground temperature calculated with interior temperature minus 2ºC Infiltrations DB 6 + Infiltration Internal gains DB 7 + Internal gains Surface convection DB 8 + Surface convection CIBSE algorithm Surface properties DB 9 + Ground floor solar absorbtance Glazing properties DB 10 + Glazing solar factor and glazing U value changed to account for blinds CALIBRATED MODEL DB 11 + Ground temperature calculated with interior temperature minus 2ºC EXTENDED MODEL CM-1 + DOE-2 and TARP convection algorithm CM-1 + Weather data file TMY EXTENDED MODEL CM-1 + DOE-2 and TARP + TMY file

3. Presentation of results Figure 2 and 3 show the results of the Calibration Process. They present the gains and losses of the EW house for the winter season, for both the Base Model and Calibrated Model in comparison with the Reference Model (CCTE1). The values are expressed in KWh-year. The percentage difference for each loss and gain concept has also been included. By comparing both graphs we can observe that differences were reduced. Table 2 analyses the performance of the EW house in relation to the LW house. It shows the heating, cooling and total demand for the LW and EW house for the Reference Model, as well as the Calibrated Model and Extended Model. The results of the incorporation of the two parameters in the Extended Model, the surface convection algorithms (CM-2) and the TMY weather file (CM-3), are shown separately. This allowed for evaluating their impact independently. Values are expressed in KWh/m2-year. The percentages indicate the reduction achieved by heating, cooling and total demand of the EW house in relation with the total energy demand of the LW house.

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Fig.2. Heat gains and losses for the winter season. Comparison between Base Model (BM-1-EW ) and CCTE-1 for the earthen wall house.

Fig.3. Heat gains and losses for the winter season. Comparison between Calibrated Model (CM-1-EW) and CCTE-1 for the earthen wall house. Table 2.Performance of the EW house. Heating, cooling and total demand for the LW and EW house and percentages of reduction in energy demand Heating/cooling demand (KWh/m2-year) Model name

Lightweight system

(LW)

Heating

Cooling

Total

CCTE-1

117.9

5.7

123.6

CM-1

134.2

15.3

149.5

CM-2

137.1

4.0

141.2

CM-3

113.8

29.4

143.2

EM-1

110.2

18.1

128.3

Earth wall

(EW)

Model description

Heating 111.1 (-5.5%)

Cooling 0.0 (-4.6%)

Total 111.1 (-10.1%)

118.7 (-10.4%) 131.4 (-4.1%) 94.7 (-13.3%) 89.7 (-16.0%)

1.1 (-9.5%) 0.0 (-2.8%) 6.1 (-16.3%) 2.7 (-12.0%)

119.8 (-19.9%) 131.5 (-6.9%) 100.7 (-29.6%) 92.4 (-28.0%)

REFERENCE MODEL CALIBRATED MODEL CM-1 + DOE-2 and TARP convection algorithm CM-1 + Weather data file TMY EXTENDED MODEL = CM-1 + DOE-2 and TARP + TMYfile


4. Discussion 4.1. Performance of the earthen house versus the lightweight construction system Observing the results in Table 2, it can be said that in all cases, the use of thermal mass generates a reduction in heating and cooling demand. The reduction achieved varies between each model according to the software and the parameters used. While in CCTE-1the EW house presents an overall reduction of 10.1%, in the Calibrated Model, it achieves a reduction of 19.9%, which is almost twice the benefits obtained in CCTE-1. When evaluated under the Extended Model conditions, the earthen house achieves greater improvement in relation to the lightweight house, with an overall reduction of 28% in energy demand. Although the main parameters and considerations of CCTE software where benchmarked in Design Builder models, there are differences in the heating and cooling demands between the CCTE-1 and Calibrated Model (Table 2, first and second raw). One reason could be that both softwares account for the heating and cooling demand differently. The heating demand in CCTE software is calculated directly from the heat balance. In other words, it is the sum of the heat flows into and out of the zone. Otherwise, Design Builder considers the value of the zone sensible heating as the heating effect of any air introduced into the zone through the HVAC system. This includes for example any `free heating´ due to the introduction of warm outside air. Therefore, Design Builder takes into account the complete HVAC heating contribution [18]. The reduction on energy demand achieved by the EW house in the Extended Model, which reaches 28%, is due to the incorporation of the TMY weather file and not to the use of DOE-2 and TARP convection algorithms which actually reduce the benefits of the earthen house. It can be said that CCTE software underestimates the benefit of the earthen house in reducing heating and cooling demand, when compared with the Extended Model. This is due mainly to the specific weather file utilized by CCTE for Pudahuel and not to the use of CIBSE convection algorithms. 4.2. Parameters and assumptions of software tools and their effect on the evaluation of earth construction technologies 4.2.1. Ground floor temperatures Ground floor temperatures demonstrated an important impact on the heat balance and on heating and cooling demand values. A ground temperature of 14ºC appears in the CCTE weather file for Pudahuel. As a first approach, this value was used in the Design Builder Base Model for all months. But the use of 14ºC all year around generated an important heat loss and, in consequence, an increase on heating demand. Because of this, a second approach to ground floor definition was used. The Design Builder documentation [18] recommends considering a value of 2ºC less than the average monthly indoor space temperature for each month. This approach was adopted and, in order to obtain the monthly indoor air temperatures, a model with a high insulated slab on ground was simulated once. This allowed for the reduction of losses through the ground and narrowed the difference in ground losses between the CCTE-1 and Design Builder model. The impact of this change in the relationship between the LW and the EW house, is that it produces an increase in the benefit of the EW house from 3.6% for BM-1 or Base Model, to a benefit of 11.7% for DB-6 in the reduction of total energy demand. This could be explained because the increase in the cooling demand, generated by the reduction on heat losses through the ground, is higher for the LW house than for the EW house, showing the benefits of the earthen wall thermal mass. 4.2.2. Surface convection algorithms CCTE software utilizes for interior and exterior surfaces a constant heat transfer coefficient (hc) for surface convection calculations. On the other hand, Design Builder software considers, by default TARP as the inside surface convection algorithm and DOE-2 algorithms for outside surface convection calculations. Both use variable natural convection based on temperature difference [18]. Due to the difference observed in losses through exterior

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walls in Figure 2, in the Calibrated Model the CIBSE algorithms were used for both interior and exterior surfaces. These algorithms consider a constant heat transfer coefficient. This change reduced the observed difference. If we compare CM-1 and CM-2 in Table 2, when DOE-2 and TARP algorithms are re-incorporated, the percentage of reduction in the energy demand is reduced from 19.9% to 6.9%. There is also an increase in heating demand due to an increase in losses through exterior walls. This increment is higher for the EW house than for the LW house. This suggests that although on one hand the use of CIBSE algorithms results in an increase in benefits of the EW model, on the other hand, the use of a fixed hc underestimates the losses through walls. 4.2.3. Weather file data The use of a different climatic file, generated an important difference on results. While in the Calibrated Model the percentage of reduction in energy demand is 19.9%, the use of the TMY weather file increased the benefits of the earthen house reaching a value of 29.6% in the reduction of energy demand. There is an increase in the cooling loads in both cases, when TMY file is used, but with a higher increase for the lightweight house. This could be attributed to the fact that the TMY file temperatures are higher and the benefits of thermal mass would have a greater impact under these conditions. In other words, under warmer conditions the little availability of thermal mass in the LW house produces an even higher requirement for cooling during summer. On the contrary, the CCTE weather file reduces the benefits of the EW house, reducing the cooling demand and increasing the heating demand. This suggests that the weather file utilized by CCTE software for that location represents a relatively colder weather. This could be advantageous considering that the Chilean rating system and thermal regulation aim to reduce the energy consumption of households during winter, encouraging the use of insulation to achieve this objective. Besides, having relatively colder weather, places the simulation in the worst case for winter, but it generates a reduction in the benefits of thermal mass. 5. Conclusion The use of earth walls, in the studied climatic context, is able to generate a benefit in energy demand when compared to a lightweight construction system. The use of thermal mass generates a reduction in the heating and cooling demand. CCTE software is able to address the incorporation of earthen materials and predict the benefits of the increase of thermal mass. Some parameters embedded in CCTE software can lead to an underestimation of the benefits of an earthen house, when compared with an evaluation performed with parameters considered by more advanced software tools. The specific weather file utilized by CCTE for the specific zone has proven to be an important factor that affects those results. CCTE software has been developed to assess compliance with the Chilean thermal regulation; therefore, its assumptions are in accordance with it and with a certification system based on the reduction of heating demand and the use of insulation. Under these conditions, for example, the use of a relatively colder climate is adequate, but it can be detrimental for massive constructions as the one presented in the earthen wall case study. In this sense, the study of alternative methods of evaluations for the assessment of cases that differ from common constructions systems, as earthen houses, is recommended. Finally, this research presents a first approach to the study of earthen material evaluation under the new Chilean rating system. Further studies are needed to address other locations within the country as well as a more detailed evaluation of the different earth technologies which are broad and whose characteristics can change from one to another. Studies that measure the actual performance of earthen houses should also be done, in order to validate the results obtained with the software. References [1] G. Minke, Earth construction handbook: the building material earth in modern architecture. UK : WIT Press, 2000. [2] R. Rael, Earth architecture. New York : Princeton Architectural Press, 2009. [3] S. Goodhew, R. Griffiths, Sustainable earth walls to meet the building regulations. Energy and Buildings. 37 ( 2005) 451-459. [4] M. Hall, R. Lindsay, M. Krayenhoff, Modern earth buildings: materials, engineering, construction and applications. Oxford : Woodhead Pub

María José Moreno and Francesco Fiorito / Procedia Engineering 180 (2017) 502 – 509 Ltd, 2012. [5] E. Kossecka, J. Kosny, Effect of insulation and mass distribution in exterior walls on dynamic thermal performance of whole buildings. Conference proceeding: Thermal Performance of the Exterior Envelopes of Buildings VII, December 6-10, 1998. [6] J. Kosny, T. Petrie, D. Gawin, P. Childs, A. Desjarlais, J. Christian, Energy benefits of application of massive in residential buildings. Conference proceeding: Thermal Performance of the Exterior Envelopes of Whole Buildings VIII, 2001. [7] S.A. Kalogirou, G. Florides, S. Tassou, Energy analysis of buildings employing thermal mass in Cyprus. Renewable Energy. 27 (2002) 353– 368. [8] K. Gregory, B. Moghtaderi, H. Sugo, A. Page, Effect of thermal mass on the thermal performance of various Australian residential constructions systems. Energy & Buildings. 40 (2008) 459-465. [9] L. Zhu, R. Hurt, D. Correia, R. Boehm, Detailed energy saving performance analyses on thermal mass walls demostrated in a zero energy house. Energy and Buildings. 41 (2009) 303-310. [10] C. Saldanha, J. Piñon, Influence of Building Design on Energy Benefit of Thermal Mass Compared to Prescriptive U-Factors. Conference proceeding: Thermal Performance of Exterior Envelopes of Whole Buildings XII, 2013. [11] X. Dong, V. Soebarto, M. Griffith, Strategies for reducing heating and cooling loads of uninsulated rammed earth wall houses. Energy and Buildings. 77 (2014) 323-331. [12] D. Allison, M. Hall, Hygrothermal analysis of a stabilised rammed earth test building in the UK. Energy and Buildings. 42 (2010) 845–852. [13] S. Liuzzi, M. Hall, P. Stefanizzi, S.P Casey, Hygrothermal behaviour and relative humidity buffering of unfired and hydrated lime-stabilised clay composites in a Mediterranean climate. Building and Environment. 61 (2013) 82 - 92. [14] MINVU, CCTE v2.0 Manual del Usuario. Santiago de Chile : MINVU, 2009. [15] R. Rioseco, C. Tesser, Cartografía interactiva de los climas de Chile. [Online] http://www7.uc.cl/sw_educ/geografia/cartografiainteractiva/. [16] W. Bustamante, Guía de diseño para la Eficiencia Energética en la vivienda social. Santiago de Chile : MINVU, 2009. [17] W. Bustamante, F. Encinas, Y. Rozas, F. Victorero, Manuales de referencias tecnicas: fundamentos tecnicos. Santiago de Chile : PUC, 2007. [18] DesignBuilder. Design Builder v3.0 Simulation Documentation. [Online] 2011. http://www.designbuilder.co.uk/helpv3/.

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