An integrated approach of building information modelling and life cycle assessment (BIM-LCA) for gas and solar water heating systems

Abstract

Buildings are responsible for the energetic consumption and potential greenhouse gas emissions during their life cycle. Water heating system contribute to a building’s energetic consumption, mainly in residential units, throughout the building’s operational phase. Variability in energy sources, reservation and distribution systems of hot water along with the types of construction materials used in these building systems are key decisions to make in the initial design phases of a building project. Often, the definition of the most appropriate water heating system for a building is made via a technical-economic decision. However, the decision is rarely based on natural resource consumption and environmental impact generation throughout the life-cycle of the heating systems and of buildings as a whole. This study presents an application of a specific environmental management tool, based on an integrated Building Information Modelling (BIM) and Life-Cycle Analysis (LCA) method for selection of hot water systems, during the early design building phase. The proposed approach is implemented in the pre-operational phase, in order to enable decision makers to appreciate the resulting environmental performance of water heating systems in buildings. The applicability of the framework is tested via a comparative study of solar heating water systems and natural gas heating water systems for a residential multifamily building to be constructed in Rio de Janeiro, Brazil. For the indicators damage to human health and damage to ecosystem, results indicate that the greatest impact on global warming comes from the natural gas heating system, while for solar heating, free particulate matter was the highest negative contribution. The operation phase for the natural gas system was highest for climate change while for solar heating system, it was the fresh water that was impacted the most during the pre-operational phase of the system’s use.

Keywords:

• Life cycle assessment methodology
• hot water building systems
• environmental performance
• building information modelling

Introduction

The construction industry is regarded as a highly polluting sector worldwide (Han et al. 2022). Buildings consume around 40% of the global energy (Hamida et al. 2021a), 25% of water, 40% of resources and are responsible for about 30% of greenhouse gas (GHG) emissions (UNEP 2011). Such environmental impacts are expected to increase with the expansion of urban areas and with further economic growth and improvement in standards of living (Wang and Lee 2022). One approach of curtailing the energy expended by building is through enhancing the performance of buildings via analyzing several energy systems such as water heating, cooling, lighting and power use by other appliances (Brounen et al. 2012; Hassan et al. 2014; D'Agostino et al. 2022). Critical challenges exist for the Latin American construction industry due to the wide diversity of climatic zones requiring distinct standards that add to the complexity of developing adequate energy efficient buildings, and the lack of awareness of consumers and construction companies regarding the advantages of energy efficiency in buildings (Morgado 2015). There is thus an urgent need to mitigate the consumption of resources and energy over the entire lifespan of buildings in order to improve the environmental performance of buildings and to protect the built environment (Aghimien et al. 2022).

Brazil is a country that is mostly dominated by electricity consumption. In particular, residential buildings in Brazil are responsible of around 30% of the electric energy consumption (EPE. 2018), where the installation of water heating system is a necessity inherent in such types of buildings (Lucchesi et al. 2017). A report by Furlanetto and Possomai, found that over 25% amount of energy consumed is utilized in water heating systems in residential buildings (Furlanetto and Possamai 2001). Electric showers are commonly adopted in Brazil in a bid to bring down energy costs for residential households (Bessa and Prado 2015). Alternative systems exist that are based on more environmentally-friendly energy sources (Solangi et al. 2011; Kern et al. 2021). For instance, gas and solar water heating systems are reported as viable alternatives in the literature (Islam et al. 2013; Wilson et al. 2013; Jamar et al. 2016). The decision of choosing the best water heating system is generally based on economic and technical information, disregarding the environmental performance of the installations and the associated impacts of operating the system (Halawa et al. 2015; Sun et al. 2015; Gautam et al. 2017). The application of an environmental management method such as Life Cycle Assessment (LCA) could empower the decision-making process concerning the use of heating system in buildings based on sustainable development criteria (Kulczycka and Smol 2016; Garcia-Herrero et al. 2017). In particular, LCA helps focus the decision making process at an early stage of building design, where collecting and evaluating the environmental impacts over the entire lifespan of the analyzed product is still valid (Tushar et al. 2021; Hamida et al. 2021b).

LCA is defined as a methodology to measure possible environmental impacts associated with all life stages of a product (Guillén-Lambea et al. 2021; Ji et al. 2020). According to ISO 14040 and 14044, it involves four general phases (ISO 2006a, 2006b) namely: i) Goal and Scope; ii) life cycle inventory (LCI); iii) Life Cycle Impact Assessment (LCIA) and iv) Interpretation. Goal and Scope deals with the definitions of the objectives of the study, where the decision maker needs to highlight the focus of the study, the boundary limits of the study, the type of product system considered, definition of the function and functional unit and other general definitions important to the analysis. In LCI, all information related to the life cycle process and defined product system is collected and organized. In LCIA all the data obtained in the previous stage i.e., LCI is classified according to impact categories; this permits the verification of the influence of the product system on the environment under different pre-defined environmental aspects. Finally, the Interpretation phase is related to the analysis of the output obtained, where expected results are compared to those that already exist, along with evaluating the need for further refinement in the factors.

LCA has several variants that depend on how the boundary of the study is defined (Sandanayake et al. 2022). The definition of the boundary of the study is attributed to the life cycle process, where a product can be looked at from the start of its raw material extraction process, to its delivery as a final product to manufacturers. Alternatively, the boundary can be extended further to cover the final stages of the product, involving either its recycling or disposal. The most systemic approach of LCA is known as cradle to the grave, in which data are collected at all stages of the product's lifespan, starting from the extraction of raw materials, fabrication, distribution, and ending with its final use and disposal/recycling/reuse (IES. 2010; Cabeza et al. 2014; Klopffer 2014; Filho et al. 2016).

Building Information Modeling (BIM) is a tool that aims to improve the coordination and collaboration between the designing team to facilitate the delivery of construction projects (Chan et al. 2019; Meng et al. 2020; Shukra and Zhou 2021). This tool enables the assessment of energy consumption in buildings (Sanhudo et al. 2021). It has been indicated to be integrated with LCA to improve the energy performance and evaluate the environmental impact towards sustainable construction projects (Ahmadian et al. 2017; Ji et al. 2020). In Marzouk et al. (2018), BIM was combined with LCA to select optimum building systems taking into consideration stochasticity in life cycle costing. In Eleftheriadis et al. (2018), BIM was integrated with LCA in order to structurally optimize concrete buildings based on embodied carbon. A review on use of BIM across a project’s life cycle to assess the performance of buildings was presented in (Jin et al. 2019), BIM and LCA were combined in Santos et al. (2020) to determine environmental, economic, and physical information of office buildings in Western Europe. A roadmap for integrating BIM into a project’s life cycle was presented in (Ma et al. 2018). Renovation decisions in buildings were examined through their greenhouse gas impacts by using BIM and LCA in Feng et al. 2020.

This study adopts the cradle-to-grave approach of LCA in order to contrast the environmental performance of two different Hot Water Building Systems (HWBS), namely Natural Gas (NG) and a Solar Heating (SH) system that is complemented with use of electricity. There is currently an insufficient database of resource consumption and environmental and energy impacts in Brazil (Willers and Rodrigues 2012). As such, another goal of this work is to develop an environmental assessment method applicable to a wide range of materials used in hydraulic systems adopted in domestic water heating systems in Brazil. A final aim of this study is to present the integration of the LCA approach with BIM for better visualization and quantification of data analyzed. It is expected that the developed inventory database and LCA-based framework will encourage decision makers in Brazil’s construction industry to consider environmental impacts associated with the choice of water heating systems.

In the next section, the LCA approach, organized into nine distinct phases, will be presented in order to simplify its application to building water heating systems. The framework is then later validated on a case study of a multi-family residential development located in a large Brazilian urban center, comparing a piped NG water heating system with SH that uses thermal heaters located on the roof of the building. Discussion of results follows. Finally, concluding remarks are presented at the end.

Materials and methods

The application of LCA methodology

The proposed method was structured according to nine main phases, which guide the preparation and evaluation of the projects and their respective analysis, as demonstrated in Figure 1. Particular emphasis targets transforming the Interpretations phase of LCA into a more in-depth analysis in order to delineate a complete process for carrying out a rigorous analysis that is applicable for water heating systems. A summary of the phases of the method developed, grouped into 4 stages for ease of tracking the steps involved, is as follows. First, the Definition of the Objective and Scope (A) involves defining the water heating system analysed, along with defining the main impact of heating system products that need to be examined for life cycle impacts. Second, an Interpretation or Stakeholders' (A) phase follows, which aims to discuss with everyone involved in the construction project on their needs in terms of environmental performance for the project, in accordance with the definitions in the first phase. Third, a Definition of the Objective and Scope (B) phase follows, which is related to the function determinations, functional unit, product system, and a further refinement of the scope of the study in accordance with the suggestions made by stakeholders in the second phase. Fourth, an Interpretation (B) phase is implemented, to validate all data obtained so far. Fifth, the Preliminary Development of Projects phase involves qualitatively and quantitatively identifying the relevant construction materials involved for each system analysed, achieved through the use of a BIM platform to assist in a better visualization and accurate representation of data. Sixth, Inventory analysis is conducted to to collect all the data of the flows involved in the phases determined by the product system. Seventh, an Interpretation (C) phase is implemented, involving a qualitative correlation phase between the elementary flows of the product system processes and the information obtained by inventory in the sixth phase. This acts as a validation step before proceeding with the study. Eighth, an Assessment of Life Cycle Impacts is conducted based on the data collected in the previous phases. This phase involves calculating and classifying of data under predefined impact categories, through use of a known database such as Ecoinvent (Wernet et al. 2016) and the aid of software for the Assessment of Life Cycle Life, in order to obtain more credible outputs. LCIA in this phase is conducted via ReCiPe 2016 method to translate environmental impacts into scores via characterization factors (Frischknecht and Rebitzer 2005). In the ninth phase, an Interpretation (D), is conducted to analyze the results of the LCIA obtained in phase eight and verifies the possibility of the study being applicable in other cases.

Figure 1. General flowchart of application of the method; labels A,B,C,D are stages that group the steps involve for ease of tracking the steps involved.

Tools and software requirements

In this study, it is assumed that the construction project is designed in BIM to allow a more accurate analysis of the quantities of materials involved in the project (Soust-Verdaguer et al. 2017; Ma et al. 2018; Jin et al. 2019; Najjar et al. 2022; Saepro, n.d.). The modeling of the product systems is achieved via OpenLCA software (OpenLCA, n.d.) and with the aid of the Ecoinvent database as an LCI database (Frischknecht and Rebitzer 2005; Wernet et al. 2016) the impact assessment (LCIA) can be achieved using ReCiPe (Acero et al. 2015; Huijbregts et al. 2017). In LCIA, the classification of the inventory data within the impact categories takes place, followed by their characterization (numerical indicators for each Midpoint Impact category defined as priority) and then weighting.

Application of the developed LCA method for HWBS

Goal and scope

Since the proposed LCA approach applies for HWBS’s arrangements, relevant equipment installed and preliminary piping design is required, as well as identification of device positions, namely locations of showers in each apartment, heating appliances and systems and the quantities of these items involved in a project. All of this is possible to achieve via BIM. Consumption of hot water for cooking, sinks and other secondary activities was neglected, given that it is desired to obtain only the heating performance related to the shower due to the fact that it is the largest consumer of heated water at homes (Furlanetto and Possamai 2001). Furthermore, the system boundary of this work is designed to be limited to the production and use phases of the HWPS products’ life cycles, disregarding the end-of-life phase. This is because duration of the use phase in the life cycle can be wide and varied, depending on the project type and associated use of the project. Additionally, maintenance phase of the life cycle was neglected to the limited need for maintenance of the products analysed. Figures 2 and 3 illustrate the system boundary of the study, classifying the various flows analysed across the life cycle of the HWPS products into Material Flows, Energy Flows, Water Flows and Environment Flows for both the NG and the SH products, respectively.

Figure 2. System boundary associated with Natural Gas Heating System.

As can be noticed from Figures 2 and 3, only the pre-operational and operational phases of the chosen HWBS were considered over a lifespan of 25 years, which is designated as the useful life of the products analysed; it should be noted that this value is determined mostly by the solar thermal heating product, whose life span based on the warranty of the manufacturers of solar collectors was shorter than typical NG systems (Guimarães, n.d.; Jordan and Kurtz 2012). The functional unit is configured in this study as a performance unit and defined as “the volume of water necessary to take a shower lasting for 5 minutes, at a water temperature of 40 °C in a shower accompanying the HWBS, and whose useful life span is estimated as 25 years”. This definition is in line with the habits of people in Brazil, and is considered as appropriate for rate of consumption of water and energy needed to raise the ambient temperature of water to the desired temperature of use (Guimarães, n.d.; Jordan and Kurtz 2012),

Case study

A case study is used in this section to demonstrate the proposed LCA-BIM approach. The case study chosen is a multifamily residential complex located in the central area of the city of Rio de Janeiro, called Quilombo da Gamboa. The project for the aforementioned housing complex consists of five buildings, interconnected by internal accesses and corridors on the floors. Each building has a ground floor and three standard floors, in addition to a roof with an upper reservoir and technical area. The housing units have two different types (i.e., one and two rooms) totaling 116 units distributed among the blocks as illustrated in Figure 4. The proposed method is applied to analyse the environmental performance of the HWBS used in the residential baths, with heating via NG and SH, taking into account the executive particularities of the project and peculiarities of the land site.

System boundary of products

As was depicted in Figure 2, the LCA carried out for the HWBS with heating via NG requires the consideration of a number of factors: i) the constituent materials, namely the pipelines for transporting gas and heated water, the heating devices, meter and closing devices and shower; ii) transport activities associated with the manufacturing and construction of the heating system; iii) energy; iv) waste generated; v) the system construction stage; and vi) the utilization stage, considering energy and resource consumption (Kulay et al. 2015). Doing so enables the pre-operational and operational phases and component life cycle to be analyzed, along with the associated resource consumption.

For LCA related to the HWBS built with heating via SH and electricity (see Figure 3), a similar process to that described above is followed: i) the constituent materials considered for the system and the energy source; in the case presented, the Chlorinated polyvinyl chloride (CPVC) pipes for circulation and distribution of hot water, Polyvinyl chloride (PVC) for supplying the reservoirs with cold drinking water, solar collectors, thermal reservoirs, circulation pumps, apartment water meters, general closing records and shower for bathing. It is important to note that for the SH solar radiation is combined with electricity for backing thermal reservoirs in periods of low sunshine and for feeding the centrifugal pumps for circulating the heated liquid through the collector arrangements.

Figure 3. System boundary associated with SH and Electricity.

Figure 4. 3 D visulaisation and floor plan of the case study considered.

Life cycle inventory (LCI)

For this step, it is important to determine the input and output flows for each heating system contrasted. The building system project development is summarized, taking into account the precise design and the associated material quantification for both system which is achieved via BIM as summarized below.

Determination of input and output flows

This step requires determining the reference flows, related to the inputs and outputs of the processes involved in the proposed systems regarding the materials needed for the system and its related energy resources (i.e., water consumption, energy for heating by gas or electric source, consumption of construction materials for installation). At this level of the analysis, some important requirements for the data collected by the study are to be defined such as geographical area, technologies covered, precision, completeness and representativeness of the data, data sources and information uncertainty (Haddad et al. 2013).

Geographical area plays a basic role when installing projects. This comes back to the fact that the installation of HWBS are being influenced by local conditions and climatic conditions (Silva et al. 2020). The second requirement herein is technologies covered by the collected data, taking into consideration that building systems are obtained from building materials that are the product of industrial processes (Zambrana-Vasquez et al. 2015). It is essential to highlight that these processes are translated into the product system and the data collected as being actually used by the construction material production chain, avoiding using obsolete or underused processes in practice. Precision, completeness and representativeness of data are basically important to evaluate the consumption of materials from building systems (Lasvaux et al. 2016). Hence, the use of BIM modeling has become crucial to obtain credible quantitative surveys (Najjar et al. 2019). In the Brazilian market, there is an insufficient database to cover the proposed requirements. Hence, this work has opted for the use of the global market, using Ecoinvent database. This work highlights that some approximations and deductions are necessary for the collection and treatment of data (Silva et al. 2020).

Building systems project development

At this step, the design of both the NG and SH systems are considered. Understanding the exact design of the involved water heating system ensures the accuracy of the input data of the LCA. Figure 5 summarizes the steps involved in calculating the precise materials associated with each system. To the left of Figure 5, the design of the NG water heating system is decomposed into eight steps, including determining the project the calculation of the total gas. A sketch of the gas system plant is obtained, after which the pipe diameters designed according to system arrangement is calculated, along with the pressure sizing, systems modeling, definition of materials employed and final material ratio. Similarly for the SH system, once the parameters of the product are identified, the total water demand is defined. Next, the heating power needed to heat the water demanded is obtained, followed by the annual solar irradiance that is used by the system and converted into thermal energy. The solar panels necessary to achieve the desired power can then be determined, followed by the accompanying hot water distribution and circulation pipings. Both systems are modelling in BIM at Level of Development of 4 at least in order to generate precise material quantity take-offs .For both the NG and SH systems, the output data will be input into the Life Cycle Impact Assessment, which is the subsequent phase of the study.

Figure 5. Flowchart of the project preparation process.

Table 1 summarizes the results yielded at each step involved in Figure 5 for the NG system in the case study analysed, including; definition of the project parameters; sizing of the computed gas power; sketch of the installation arrangement; dimensioning of the gas pipeline to satisfy the required power; value of water demand; dimensioning of the hot water pipe sections through the demanded flow; modeling of the installation and survey of the list of materials.

Table 1. Project preparation process for NG system.

Step		Result
I	Project parameters definition	System arrangement: 116 individual continuous flow heaters with flow of 9 L/min, 82% output and using a power of 13400 kcal/h GN – individual private system Gas meters location: ground floor public area
II	Total system power sizing	According to ABNT NBR 15528/2016 standard and local gas concessionaire standards − 1868 kcal/min.
III	Building installation plant sketch	Gas distribution network sketch and its derivations
IV	Gas piping sizing by demanded power of each consumption-site (using flows)	Gas supply piping sizing from building access to the heaters in each building apartment
V	Water demand determination	Sum of gas power downstream multiplied by a Simultaneity Factor– total gas flow 13.92 L/s
VI	Hot water piping sizing by demanded water flow per piping part	Piping sizing from heaters to consumption points (showers), by using hot water flow per point
VII	Installation modeling	System modeling using BIM
VIII	List of building materials	BIM Quantity take-off to generate the LCA Quantity inputs

The list of materials derived from BIM for the input flows of LCA for the NG system, is shown in Table 2.

Table 2. List of materials generated for NG water heating system using BIM.

Item	Description	Unit	Quantity
1	PIPING
1.1	Weldable white CPVC pipe diameter 15 mm for hot water systems	m	1043
1.2	Copper pipe type “A” diameter 28 mm	m	9661
1.3	Copper pipe type “A” diameter 54 mm	m	184
1.4	Copper pipe type “A” diameter 65 mm	m	34
1.5	Copper pipe type “A” diameter 80 mm	m	13
2	EQUIPMENT AND ACCESSORIES
2.1	Continuous flow heater	each	116
2.2	Copper globe valve 1”	each	116
2.3	Natural gas meter	each	116
2.4	Shower in ABS	each	116

Table 4 summarizes the results yielded at each step involved in Figure 5 for the SH system in the case study analysed, including; definition of the project parameters, materials which will be used in the system components; the location of the project (for obtaining local thermal and insolation information); demand for unit hot water from the devices that will compose the system; definition of the water accumulation and storage regime (Table 3).

Table 3. Project preparation process - HWBS with heating via SH.

Step		Result
I	Project parameters definition	Location: Rio de Janeiro / RJ Latitude: 22 ° 54′13 " Longitude: 43 ° 12′35 " Demand: showers with 0.12 L/ s hot water flow Arrangement: Collective central solar with electric complement Circulation: Forced, with centrifugal pump Regime: Accumulation (general thermal reservoir)
II	Determination of system’s hydraulic demand	Flow rate of use of the devices, multiplied by the time of daily use and the number of devices - Daily demand = 57.27 m³ / day
III	Hot water volume storage sizing	ABNT NBR 15569/2008 precepts, taking into account factors such as the loss of thermal energy in the hot water distribution pipe − 55 m³ of reserved water (8 reservoirs of 5 m³; 3 reservoirs of 4 m³ and 1 reservoir of 3 m³)
IV	System’s energy demand determination	Thermal difference between the water use temperature and the room temperature (the average daily room temperature was used annually) − 1982.90 kWh
V	Total solar collectors area sizing	Sizing routine of NBR 15569/2008 Total area: 608 m² (304 collectors)
V.1	Determination of the global anual irradiation average	Thermal energy − 4.58 kW / m².day
V.2	Determination of daily power production average	Energy effectively available in the water heating system − 3.62 kWh / m².day
V.3	Solar panel especifications	Model FCC220-2V Heliotek, due to the better cost benefit (lower acquisition cost for higher thermal energy generated)
V.4	Correction factor for solar panel slope and orientation	Dependent on the direction of each set of collectors
VI	Installation arrangement sketch	Drawings of sections of hot water piping circulating through the plates and distributing to consumption points
VII	Distribution piping sizing	Water distribution piping to the points (by the required flow and pressure) according to each section
VIII	Solar panel circulation piping sizing	Distribution of circulation by solar collectors according to each section
IX	Installation modeling	System modeling on BIM platform
X	List of building materials	Quantitative inputs of the Life Cycle Assessment employed

Table 4. List of materials generated for SH water heating system using BIM.

Item	Description	Unit	Quantity
1	PIPING
1.1	Weldable white CPVC pipe diameter 15 mm for hot water systems	m	3246
1.2	Weldable white CPVC pipe diameter 22 mm for hot water systems	m	663
1.3	Weldable white CPVC pipe diameter 28 mm for hot water systems	m	119
1.4	Weldable white CPVC pipe diameter 35 mm for hot water systems	m	100
1.5	Weldable white CPVC pipe diameter 42 mm for hot water systems	m	246
1.6	Waldable brown PVC pipe	m	11
2	EQUIPMENT AND ACCESSORIES
2.1	Aluminium solar panel – collector area 2 m²	un	304
2.2	Thermal reservoir 3000 with stainless steel body, thermal isolation with glass wool and electrical resistance for water heating electric power 7500 W	un	1
2.3	Thermal reservoir 4000 l with stainless steel body, thermal isolation with glass wool and electrical resistance for water heating electric power 6 × 7500 W	un	3
2.4	Thermal reservoir 5000 l with stainless steel body, thermal isolation with polyurethane and electrical resistance for water heating electric power 6 × 7500 W	un	8
2.5	Single-stage centrifugal pump for water recirculation, estimated electric power 2,0 CV, stainless steel body and bronze rotor	un	10
2.6	Copper alloy water meter ½”	un	116
2.7	Bronze Ball Valve ½”	un	116
2.8	Shower in ABS	un	116

The list of materials derived from BIM for the input flows of LCA for the SH system, is shown in Table 4.

HWBS inventory

Once the construction materials are obtained from the previous step, the inventory database of construction materials for each heating system is inventoried based on the pre-operational stage (i.e., extraction of raw materials, manufacture and transport of the components until the construction of the system), and the operational phase (i.e., consumption over the entire lifespan). OpenLCA Life Cycle Assessment software was used to perform the life cycle assessment, and Ecoinvent database was used as the LCI database. The list of design materials, considering raw materials too, for both the NG and the SH systems is summarized in Tables 5 and 6 respectively.

Table 5. Summary of materials used in HWBS with heating via NG, consumption of raw materials and manufacturing processes.

Item	Description	Unit	Constituent material	Consumption		Manufacturing Process
				Unit	Coefficient
1	PIPING
1.1	Weldable white CPVC pipe diameter 15 mm for hot water systems	m	CPVC	kg/m	0,098	PVC Chlorination
						Extrusion
						Injection (for piping connections)
1.2	Copper pipe type “A” diameter 28 mm	m	Copper	kg/m	0,463	Extrusion
						Drawing
1.3	Copper pipe type “A” diameter 54 mm	m	Copper	kg/m	1,345	Extrusion
						Drawing
1.4	Copper pipe type “A” diameter 65 mm	m	Copper	kg/m	1,829	Extrusion
						Drawing
1.5	Copper pipe type “A” diameter 80 mm	m	Copper	kg/m	2,627	Extrusion
						Drawing
2	EQUIPMENT AND ACCESSORIES
2.1	Continuous flow heater	un	Aluminium	kg	8,000	Extrusion
						Injection
			Copper	kg	4,100	Extrusion
						Drawing
2.2	Copper ball valve 1”	un	Copper alloy	kg	0,239	Casting
						Machining
2.3	Natural gas meter	un	Aluminium alloy	kg	1,200	Pressured casting
2.4	Shower in ABS	un	Painted ABS	kg	0,982	Injection
						Chromium plating

Table 6. Summary materials used in HWBS with heating via SH, consumption of raw materials and manufacturing processes.

Item	Description	Unit	Constituent material	Coefficient of consumption		Manufacturing Process
				Unit	Consumption
1	PIPING
1.1	Weldable white CPVC pipe diameter 15 mm for hot water systems	m	CPVC	kg/m	0,098	PVC Chlorination
						Extrusion
						Injection (for piping connections)
1.2	Weldable white CPVC pipe diameter 22 mm for hot water systems	m	CPVC	kg/m	0,182	PVC Chlorination
						Extrusion
						Injection (for piping connections)
1.3	Weldable white CPVC pipe diameter 28 mm for hot water systems	m	CPVC	kg/m	0,29	PVC Chlorination
						Extrusion
						Injection (for piping connections)
1.4	Weldable white CPVC pipe diameter 35 mm for hot water systems	m	CPVC	kg/m	0,462	PVC Chlorination
						Extrusion
						Injection (for piping connections)
1.5	Weldable white CPVC pipe diameter 42 mm for hot water systems	m	CPVC	kg/m	0,649	PVC Chlorination
						Extrusion
						Injection (for piping connections)
1.6	Waldable brown PVC pipe	m	PVC	kg/m	0,266	PVC Chlorination
						Extrusion
						Injection (for piping connections)
						Injection (for pipe)
						Chromium plating
2	EQUIPMENT AND ACCESSORIES
2.1	Aluminium solar panel – collector area 2 m²	un	Tempered glass thickness 4 mm	kg	20	Thermal tempering / Modelling
			Aluminium (board)	kg	4,32	Extrusion
			Aluminium (box)	m²	2	Casting
			Mineral wool	kg	0,896	Casting / Centrifugation
			Polyurethane foam	kg	3,84	Polymerization and modelling
			Copper piping	m	22	Extrusion
						Drawing
2.2	Thermal reservoir 3000 with stainless steel body, thermal isolation with glass wool and electrical resistance for water heating electric power 7500 W	un	Stainless steel plate	m²	28,978	Lamination / assembly of parts
			Glass wool	kg	64,912	Casting / Centrifugation
2.3	Thermal reservoir 4000 l with stainless steel body, thermal isolation with glass wool and electrical resistance for water heating electric power 6 × 7500 W	un	Stainless steel plate	m²	30,95	Lamination / assembly of parts
			Polyurethane foam	kg	34,664	Casting / Centrifugation
2.4	Thermal reservoir 5000 l with stainless steel body, thermal isolation with polyurethane and electrical resistance for water heating electric power 6 × 7500 W	un	Stainless steel plate	m²	36,992	Lamination / assembly of parts
			Polyurethane foam	kg	41,431	Casting / Centrifugation
2.5	Single-stage centrifugal pump for water recirculation, estimated electric power 2,0 CV, stainless steel body and bronze rotor	un	Aluminium-silicion alloy	kg	16,7	Casting
						Usinagem
						Assembly of parts
2.6	Copper alloy water meter ½”	un	Copper alloy	kg	2,6	Machining
2.7	Bronze Ball Valve ½”	un	CPVC	kg	0,1	Casting
						Injection
2.8	Shower in ABS	un	ABS	kg	0,239	Injection
						Chromium plating

Once the constituent materials for each system were obtained from BIM, their respective consumption rates, units of measure of raw materials and manufacturing process were extracted using Ecoinvent database. It is important to note that the referred consumption coefficients were calculated from the dimensional characteristics of the construction materials used in the installation and the physical properties of the raw materials such as material density, losses in industrial processes, transport processes and extraction.

Only the building construction and operational stages of the life cycle of the building project was considered. The processes involved in the construction of each system, such as the road transport of the material to the construction site along with processes directly involved with the construction of the system such as welding of parts, fixings, pipe grounding and other elements were disregarded in this analysis, due to the goal of analysis, based on LCA used as an information font for decision-making processes in project stage from buildings life-cycle – assuming that at this stage, detailed information about the disregarded processes won’t affect the comparative results for the necessary analysis depth. Taking into consideration the operational phase of the life cycle in the case study, 116 heaters installed for an average frequency of use of twelve baths per person and four people per shower for 25 years have energy demand of 8,092,988,571.42 kcal (equivalent to 9,405,851.16 kWh). Given the specific calorific value (10,000 kcal/m3) for the gas and its density under ambient conditions, the volume of natural gas required for the system is 941,045.18 m3.

For the SH system, the consumption of drinking water is considered identical to that previously calculated for the NG system, considering that the consumer population, number of consumer devices and installation location are exactly the same. Energy consumption, however, is an important variant in the process of analyzing the operational phase of the SH system's life cycle (Ramesh et al. 2010). Solar radiation energy source would be supplemented with electrical supply in periods of the year with low sunshine (Silva et al. 2020). Additionally, electrical power is considered for the set of centrifugal pumps installed for forced circulation of water by solar collectors.

The total annual deficit to be transferred to the electrical resistance system of the thermal reservoir was calculated by comparison between the sum of the average monthly energy demand for a 25 years lifespan and the average of thermal energy generated by the solar panels during the insolation period, calculated as disposed on NBR 15569 (ABNT 2008). The total annual deficit was computed as 131,919.89 kWh and the total solar energy deficit over a 25-year useful life of the system is then given by 3,297,997.37 kWh. The demand of the electrical system consists of feeding the centrifugal pumps of water circulation through the collector circuits, with a lifetime of 25 years, equivalent to 80,482.85 kWh. The energy consumption matrix of the SH system is increased in energy due to radiation associated with electrical consumption. Given the electric demand factors of the reservoirs and electric demand of the pumps, as shown in specifications for selected commercial reservoir and pumps, multiplied by the period used per day and the system’s lifespan, the total energy demand for the electrical supply is given by 3,378,479.87 kWh (12,162,527.53 MJ). As in the SPAQ with heating via Natural Gas, the system with heating via solar thermal had the data related to the life cycle of obtaining drinking water and electricity for the Brazilian matrix obtained through the Ecoinvent database. After the survey of inventory data, they were correlated to the reference flows initially defined to describe the absolute values ​​applied to the functional unit, which considers only a shower installed in in each of the 116 units of the case study building. These flows for each type of system are listed in Table 7, obtained from lists of materials of BIM modellation for each system, divided by number of showers installed.

Table 7. Reference flows for the HWBS functional units obtained via list of materials of BIM modellations per shower unit.

Item	Description	Unit	Quantity
A	HWBS WITH HEATING VIA NG
1	PIPING
1.1	Weldable white CPVC pipe diameter 15 mm for hot water systems	m	9,00
1.2	Copper pipe type “A” diameter 28 mm	m	83,28
1.3	Copper pipe type “A” diameter 54 mm	m	1,59
1.4	Copper pipe type “A” diameter 65 mm	m	0,29
1.5	Copper pipe type “A” diameter 80 mm	m	0,11
2	EQUIPMENT AND ACCESSORIES
2.1	Continuous flow heater	un	1,00
2.2	Copper ball valve 1”	un	1,00
2.3	Natural gas meter	un	1,00
2.4	Shower in ABS	un	1,00
3	WATER AND POWER DEMAND
3.1	Water estimated demand for 25 years of system operation	m³	2.252,53
3.2	Gas power estimated demando f 25 years of system operation	kcal	81,084,92
B	HWBS WITH HEATING VIA SH
1	PIPING
1.1	Weldable white CPVC pipe diameter 15 mm for hot water systems	m	27,98
1.2	Weldable white CPVC pipe diameter 22 mm for hot water systems	m	5,72
1.3	Weldable white CPVC pipe diameter 28 mm for hot water systems	m	1,03
1.4	Weldable white CPVC pipe diameter 35 mm for hot water systems	m	0,86
1,5	Weldable white CPVC pipe diameter 42 mm for hot water systems	m	2,12
1.6	Waldable brown PVC pipe	m	0,10
2	EQUIPMENT AND ACCESSORIES
2.1	Coletor solar área coletora 2 m²	un	2,62
2.2	Thermal reservoir 3000 with stainless steel body, thermal isolation with glass wool and electrical resistance for water heating electric power 7500 W	un	0,01
2.3	Thermal reservoir 4000 l with stainless steel body, thermal isolation with glass wool and electrical resistance for water heating electric power 6 × 7500 W	un	0,03
2.4	Thermal reservoir 5000 l with stainless steel body, thermal isolation with polyurethane and electrical resistance for water heating electric power 6 × 7500 W	un	0,07
2.5	Single-stage centrifugal pump for water recirculation, estimated electric power 2,0 CV, stainless steel body and bronze rotor	un	0,09
2.6	Copper alloy water meter ½”	un	1,00
2.7	Bronze Ball Valve ½”	un	1,00
2.8	Shower in ABS	un	1,00
3	WATER AND POWER DEMAND
3.1	Water estimated demand for 25 years of system operation	m³	2252,53
3.2	Electricity power estimated demand for 25 years of system operation	MJ	104849,38

Life cycle impact assessment

This study observes all the categories analyzed in the ReCiPe 2016 methodology (Huijbregts et al. 2017) for conducting the LCI. Characterization factors are applied to quantify the potential pollutants using a midpoint approach. The characterization is used to classify the data collected in inventory phase in the many midpoint impact categories of the ReCiPe methodology, such as global warming and ozone depletion and then, with the quantities of potential pollutants defined, then the damage in human health, ecosystems and resource depletion is calculated to give the notion of the potential damage over a 100-year time horizon.

Results and discussion

The next step after modeling the product systems using OpenLCA software, and the Ecoinvent database, is to conduct an impact assessment, LCIA to evaluate the associated environmental impacts for each heating system analyzed above through the ReCiPe method. The ReCiPe Midpoint methodology was first applied to analyze the main causes of the single impacts generated and to compare the results with the expectations based on previous studies; later, the Endpoint approach was used to provide additional information on the three categories of environmental impacts namely human health, ecosystems or resource depletion. Conversion from midpoint to endpoint allows simplification in the result interpretation. The ReCiPe method takes into consideration the steps of classification, characterization and weighting of the data in an impact modeling with a range of 100 years. The subsections below outline each of the three endpoint areas of prediction. The impacts are assessed based on the Disability-Adjusted Life Years (DALY) unit measure

Endpoint 1: damage to human health

The results obtained for the damage to human health caused by the water heating systems is presented in Figure 6. It is noted that the impact categories that most have implications for human health, for both water heating systems are related to global warming, fine particulate matter formation, human carcinogenic and non-carcinogenic toxicity and water consumption. The impacts of ozone formation, ionizing radiation, and ozone depletion do not contribute significantly to the overall impact and have therefore been excluded from the graphs. However, its impacts were included in the total impact sum.

Figure 6. Comparison of impacts related to damage to human health for HWBS via SH with electricity and HWBS via NG.

Concerning global warming, there is clearly a greater contribution (about 2 times more) of the NG water heating system (2.54E-02 DALY) in contrast to the SH system (1.25E-02 DALY); this is related to the main energy source used by the NG system, namely gas, which like other fuels, consists of fossil material obtained by oil extraction and processing operations, activities closely linked to global warming, and to greenhouse gas emissions. On the other hand, the SH system, has as its primary source of energy, a clean and independent source of direct emissions (electricity acting as a supplementary energy source only when needed). The SH system's contribution to global warming can be directly associated with electricity consumption and the infrastructure of this chain, as well as with the necessary infrastructure installed directly for the system to function, such as exclusive PVC and CPVC pipes, the manufacture of the solar collectors themselves and their components, and the transport chain associated with them.

In terms of the fine particulate material formation, the NG system is better compared to the SH system (contribution of 1.12E-02 DALY and 1.70E- 02 DALY, respectively). Such results are mostly driven by the necessary infrastructure requirements associated with each system and their entire production chain, rather than the direct consumption of the fuel necessary for the generation of thermal energy for the systems. As such, for the SH system, it consumes greater quantities of materials necessary to produce its infrastructure contrasted with the NG system.

In terms of human carcinogenic and non-carcinogenic toxicity, the third and fourth categories that contribute the most to damage to human health, there is also a notable difference between the systems; in the case of carcinogenic toxicity, the system that contributes the most is the SH (4.40E-03 DALY), while in non-carcinogenic toxicity, it is the system with NG heating (7.02E-03 DALY).

In terms of water consumption related to damage to human health, it is noted that the SH system contributes much more aggressively than the NG system (contributions of 2.29E-03 DALY and 7.02E-04 DALY respectively), a factor that, supposedly, must be associated with the consumption of electric energy and the production matrix of this energy, predominantly the hydroelectric generation of electricity in Brazil. The contribution of SH and NG systems for damages to human health correspond, respectively, to 4.04E-02 DALY and 4.72E-02 DALY.

Endpoint 2: damage to ecosystems

The results obtained for damage to ecosystems clearly show that SH system, although with electrical complementation, is more environmentally favorable (contributes 50,50% to the damage to ecosystems, while NG contributes 76,75% to the damage to ecosystems). This is because the impact of greater relevance consists of global warming which is highly contributed to by the fossil fuel used in NG water heating systems; in particular, the NG has an influence approximately 100% more if compared to the SH system, as presented in Figure 7.

Figure 7. Comparison of impacts related to damage to ecosystems for HWBS via SH with electricity and HWBS via NG.

It is also clear that the contribution of global warming to damage to ecosystems in both heating systems is much higher than the other impacts. In the case of SH, global warming represents 50.50% (3.78E- 05 species/year) of the contribution to the damage to ecosystems, while NG contributes 76.75% (7.67E-05 species/year), a value greater than the sum of the contribution of all the other observed impacts. The categories damage to freshwater ecosystems by global warming, and water consumption, land use, damage to marine ecosystems by eutrophication and ecotoxicity were barely represented in Figure 7 given their low contributions.

In absolute terms, the contribution of the SH system on the damage to ecosystems constitutes 7.49E-05 species per year, while the contribution of NG is 9.99E-05 species per year; this is 33% higher contribution by the NG system. This factor can be directly associated with the energy consumption of the phase of use of the systems since the NG system consumes fossil fuels for operation. In addition to this, it is clear that the infrastructure and materials necessary for the operation of the systems (piping, collectors, reservoirs, etc.), as well as their production chain, do not significantly contribute towards the impacts on the ecosystems since NG system consumes much less building materials than the SH system, and yet it has the larger detriment on the ecosystem.

Endpoint 3: resource depletion

Regarding the depletion of fossil and mineral resources, reported in the monetary value of US dollars ($) in 2013, it is clear that mineral resources do not contribute significantly in comparison with the depletion of fossil resources, as disposed in Ecoinvent database. The monetary value for consumption of the gas system is set at US $3399 for the depletion of fossil resources and US $18 for the depletion of mineral resources. For the solar system, the depletion of fossil resources is at US $948 while for depletion of mineral resources it is set at US $11. In this way it can be confirmed that the SH system shows a clear advantage in this category.

Analysis of the main sources of impacts

Using the ReCiPe midpoint method, the most relevant categories are examined further including: i) climate change, in line with the use of different energy sources; ii) depletion of fossil resources, as the energy matrix encompasses energy production from petroleum products and they are also used as raw material for the production of the building materials of the water heating systems as well as fuel for transportation; iii) human toxicity; iv) ozone depletion; v) terrestrial exoticist; vi) ecotoxicity of fresh water and vii) water consumption. It is important to note that the analysis considers the water heating systems as having a cut-off life cycle at the end of their useful life without considering the post-operational phase of the systems and their disposal (cradle-to-gate); this can be justified as the systems have a long longevity.

Analysing the contribution of the existing flows and processes in the product systems determined from LCIA midpoint calculations, a qualitative classification of these processes was carried out according to four distinct phases of the systems life cycle: pre-operational phase (represented by the production of the building materials components of the water heating systems and the construction of the system itself, along with the energy production that feeds these processes and the system itself) and operational phase (phases of energy consumption and generation of water and sewage for treatment). Figure 8 shows the contribution of each phase of the life cycle, in a standardized way, to the main environmental impact categories listed above, for the case of HWBS with heating via NG.

Figure 8. Environmental impacts related to HWBS via NG according to phases of the product system under study.

As indicated in Figure 8, the vast majority of impacts related to climate change are associated with the energy consumption of the operational phase, a factor closely linked to the consumption of natural gas as a fuel source for heaters installed in the system. This in turn feeds a chain of extraction, processing and transportation of oil products in the national matrix. In the case of depletion of fossil resources, depletion of the ozone layer and terrestrial ecotoxicity, there is also a great participation of the energy production chain in the impacts generated by the gas system. With regard to water toxicity and human toxicity, there is a significant contribution in the pre-operational phase of production of construction materials and along with energy production, both related to the industrial processes involved in the extraction, transportation, processing and distribution of materials. Production of toxic components takes place in these process along with the waste that results from the production of PVC, CPVC and copper pipes that are widely used in the water heating systems analysed. With regard to water depletion, there is a large share of the operational phase, mainly due to the generation cycle of domestic sewage inherent in the final use of the bathing system, which, in the case of the greater Rio de Janeiro, can be discarded in basins of rivers and maritime outfalls without adequate tertiary treatment.

Figure 9 shows the contribution of each phase of the life cycle, in a standardized way, for the environmental categories listed above. It is noted that, after the classification of the processes involved in the impacts generated by the system, there is a large contribution of energy production, which is mainly justified by the use of electrical energy as the supplementary source to the system, necessary for its operation in times of insufficient sunlight to meet the demand. Results of the ecotoxicity, the depletion of water, and the depletion of the ozone layer are due to the national energy production matrix in Brazil which relies on the use of hydroelectricity. These impacts are however less than that would have been created by other sources of electrical generation such as natural coal plants. Furthermore, energy production can be intrinsically linked to the production chain of the materials used in the system and supply of the production lines, since, for SH water system, the necessary infrastructure is more robust.

Figure 9. Environmental impacts of SH system, classified according to pre-operational, operational, and post-operational phases.

Conclusions

This study proposed a framework based on Life Cycle Assessment (LCA) in order to compare natural gas and solar water heating systems for buildings. The framework relies on the integration of building information modelling (BIM) for extraction of quantities associated with each system. Environmental performance assessed was with respect to impacts of consumption of energy resources and emission of greenhouse gases.

The solar heating system, although potentially less polluting in use, has a greater demand for materials for installation and use including solar collectors installed on the roof of buildings, circulation pipes with thermal insulation, pumps for circulation and general reservoirs common to the whole building, along with a supplementary power supply in case the thermal energy collected by the plates is not enough to heat the water to the ideal temperature. As such for the solar heating system, the pre-operational, extraction and manufacturing phase of the component materials were significantly environmentally impacting. In addition, the size of the building system has a direct influence on the potential environmental impacts it can cause, since Solar Heating needs a much more robust installation infrastructure than the heating system via Natural Gas, a factor that can weigh on its performance. On another hand, the gas system uses a fossil heating source, which has a potentially polluting production chain. An analysis that encompasses the entire useful life tends to favor the application of the solar system based on the case study implemented.

The method developed here, therefore, created a work routine for assessing the life cycle of hydraulic systems in buildings and this can be further extended for the purpose of obtaining information that leads to decision making at the level of developing more sustainable projects. Through the results of the evaluation, comparative environmental parameters of different water heating systems were defined, in this case, for Hot Water Building Systems with Natural Gas Heating and Hot Water Building Systems with Solar Thermal Heating. Such results in the future can be further complemented with information on initial investment and operating costs so that, in the design of the systems, the designer has tools in hand to decide, together with the other stakeholders in the process, on which final configuration to adopt for the building. Some limitations of this study include also considering the use of other international databases apart from Ecoinvent, considering other worldwide market apart from Brazil, the omitting of factors related to the architectural layout of the buildings and how that influences the facilities installed, the place of application and the availability of resources used to construct the heating systems, as well as location impact of raw materials and how the distances of extraction, manufacture, distribution and consumption creates environmental impacts.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors want to acknowledge the CNPq (Brazilian National Council for Scientific and Technological Development) and FAPERJ (Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro).