Scholarly article on topic 'Energy and Environmental Performance Analysis of Biomass-fuelled Combined Cooling and Heating System for Commercial Building Retrofit: An Italian Case Study'

Energy and Environmental Performance Analysis of Biomass-fuelled Combined Cooling and Heating System for Commercial Building Retrofit: An Italian Case Study Academic research paper on "Earth and related environmental sciences"

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{"Biomass heating and cooling (BHC)" / "Absorption chiller" / "Life cycle assessment (LCA)" / "Greenhouse gas (GHG) emission" / "Climate change" / "Environmental sustainability"}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — Elisa Moretti, Marco Barbanera, Daniele Foschini, Cinzia Buratti, Franco Cotana

Abstract This study focuses on the operating performance of a biomass boiler (100kW) coupled with an absorption chiller machine at the service of a commercial building in central Italy. A detailed life cycle environmental assessment (LCA) was performed by comparing the biomass-fuelled system to conventional system, using the SimaPro software. To assess the environmental impact, experimental data, such as energy consumptions and emission factors of the biomass boiler, were used as input data. Biomass-fuelled system was found to have the lowest impact in cumulative energy demand (CED), global warming potential (GWP), and ReCiPe single score method.

Academic research paper on topic "Energy and Environmental Performance Analysis of Biomass-fuelled Combined Cooling and Heating System for Commercial Building Retrofit: An Italian Case Study"

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Energy Procedia 101 (2016) 376 - 383

71st Conference of the Italian Thermal Machines Engineering Association, ATI2016, 14-16

September 2016, Turin, Italy

Energy And Environmental Performance Analysis Of Biomass-fuelled Combined Cooling And Heating System For Commercial Building Retrofit: An Italian Case Study

Elisa Morettia, Marco Barbanera^*, Daniele Foschinib, Cinzia Burattia, Franco Cotanaa

aDepartment of Enginnering -University of Perugia, Via G. Duranti 93, Perugia 06125, Italy bUniversity of Perugia - CIRIAF "Interuniversity Research Center on Pollution and Environment "Mauro Felli, Via G. Duranti 63, Perugia

06125, Italy

Abstract

This study focuses on the operating performance of a biomass boiler (100 kW) coupled with an absorption chiller machine at the service of a commercial building in central Italy. A detailed life cycle environmental assessment (LCA) was performed by comparing the biomass-fuelled system to conventional system, using the SimaPro software. To assess the environmental impact, experimental data, such as energy consumptions and emission factors of the biomass boiler, were used as input data. Biomass-fuelled system was found to have the lowest impact in cumulative energy demand (CED), global warming potential (GWP), and ReCiPe single score method.

© 2016 PublishedbyElsevierLtd. This isanopenaccess article under the CC BY-NC-ND license

(http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the Scientific Committee of ATI 2016.

Keywords: Biomass heating and cooling (BHC); Absorption chiller; Life cycle assessment (LCA); Greenhouse gas (GHG) emission; Climate change; Environmental sustainability.

1. Introduction

The building sector is one of the major contributor to both energy consumption and environmental pollution in the EU, accounting for up to 40% of the European primary energy use and being responsible of 36% of European Union's total CO2 emissions [1]. Several strategies can be employed to reach the energy consumption of the building

* Corresponding author. Tel.: +39 075-5853812; fax: +39 075-5153321 E-mail address: marco.barbanera@unipg.it

1876-6102 © 2016 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 Scientific Committee of ATI 2016.

doi: 10.1016/j.egypro.2016.11.048

life cycle, including the introduction of renewable energy systems based on biomass conversion technologies. The increase of biomass exploitation can contribute to the achievement of the European targets by 2020, in terms of environmental protection in energy production [2]. Bioenergy actually accounts for nearly 62% of renewable energy in the EU [3] and the European Environmental Agency foresees that the European Union primary energy requirement would be at 1.8 billion toe in 2020, 13% (or 236 million toe) of which would come from biomass contribution [4]. As a feedstock for heating and cooling production, biomass is characterized by several advantages over fossil fuels. It is widespread in many different areas and it can easily be stored, transported, and used in applications on site [3]. From the environmental point of view, biomass is considered to be a carbon neutral energy source, since the amount of the released carbon, during the energy conversion process, is similar to the amount absorbed during its life time [5]. However some environmental issues need to be evaluated in order to compare the overall impact of bioenergy to that of fossil fuels. The air emissions for instance of various pollutants, such as, NOx, CO, and particulate matter, during the use of biomass should be taken into account, representing a relevant environmental issue [6].

Global methodologies such as the Life Cycle Assessment (LCA) are appropriate tools to quantify the energy and the environmental impacts of products and services, and to compare the performance of different products or technologies that provide the same service [7, 8]. Although environmental monitoring is widely carried out by Environmental Agencies in urban areas in order to analyze the burdens and the consequences of combustion processes on human health and the ecosystem, only a few studies in the Literature employed a life cycle approach when focusing on wood biomass heating systems [6]. In particular, these studies evaluate the environmental impact of wood-based heating systems for the household sector, while, to best of our knowledge, no studies on the LCA biomass boiler units in industrial and commercial buildings have been yet reported in Literature.

The aim of the present work is to assess and compare the environmental burden of a biomass heating and cooling (BHC) system for a commercial building, located in Central Italy, with the stand-alone generation, based on fossil fuels. A BHC system satisfies space heating by a biomass boiler and space cooling by means of an absorption chiller coupled to the same biomass boiler. The system was investigated on annual basis, in terms of energy and environmental analysis. In particular, the energy consumption of the building for heating and cooling purposes was monitored during one year from January 2015 to December 2015.

2. Materials and methods

2.1 Case study description

The investigated heating and cooling system was developed in Sant'Andrea delle Fratte, the most important commercial/industrial estate in Umbria, in central Italy, characterized by massif use of fossil fuels for heating and cooling (methane is the most commonly used fuel for heating, whereas small split-units provide cooling), within the SCER (the Italian acronym for Development of a Renewable-Energy air-Conditioning Systems) research project. In the project, co-funded by the Italian Ministry for the Environment, two pilot systems were designed and set up in order to upgrade non-residential buildings with high-efficiency heating and cooling systems, which use a mix of renewable energy sources. In this work only the prototype plant with a BHC system was investigated [9, 10].

The investigated building has different conditioned zones: an exhibition room (318 m2), offices and restrooms (60 m2), a dealership (24 m2), and a mechanic's workshop (about 158 m2, 7 m high), for a total air-conditioned volume of about 2800 m3. Before the renovation, mono-split air to air heat pumps were used for cooling in some zones, whereas a methane boiler with fan-coils and radiators provided heating. After the renovation, a boiler, coupled with an absorption machine, provides both heating and cooling, using local wood-based biomass: fan-coils (in the offices) and mixing air distribution systems (in exhibition room and mechanic's workshop) were used; moreover, a 83 kWp photovoltaic polycrystalline plant installed on the roof supplies energy to cover the absorption machine and other electrical appliance needs. The features of the new heating and cooling system are shown in Table 1. The system has been working since June 2013 and the performance has been monitoring via a custom data acquisition system. It can store all the variables registered by several sensors, such as: power and energy supplied to the hot water by the biomass boiler; exhaust temperature and flow/return water temperatures in the biomass boiler; temperature and pressure of the utility buffers; working temperatures and flow rates of the absorption machine, water consumption in

the evaporative tower; status, flow rate, and water temperature of all pumps; cooling capacity and energy supplied from the chiller; total electric power and energy supplied to the system; status and temperatures of fan-coils and mixing air distribution systems; indoor air temperature; external temperature.

Table 1. The case study: features of the new biomass heating and cooling (BHC) system

Technical data

Pictures

Biomass boiler

• FIREMATIC 100 Biocontrol by HERZ Energietechnik GmbH

• Biomass Storage (chip-wood): 20 m3

• Thermal Power: 100 kW

• Max Temperature water: 106 °C

• hot buffer: volume of 1000 l

Absorption • Monobloc chiller Systema SYBCTDH70

Chiller • Water and lithium-bromide absorption cycle

• Cooling Power: 45 kW (water temperature >98 °C)

• Air/water cooling tower incorporated in the machine

• Inverter control for controlling the power (from 100% to 20%)

• Cold buffer: volume of 500 l, between the chiller machine and the fan-coils

2.2 Goal and scope definition

The main goal of this study is to carry out an environmental evaluation of the replacement of the traditional heating and cooling system in commercial buildings, based on natural gas boiler and air-air heat pump system, by a BHC system. The analysis was carried out according to the LCA methodology, which is regulated by the ISO 14040 [11] and 14044 [12] international standards. It includes four phases, namely goal and scope definition, life cycle inventory, life cycle impact assessment (LCIA), and interpretation. The Simapro 8.0 software was employed to conduct the LCA analysis. In this study only heating and cooling devices of the BHC system were taken into consideration: wood chips boiler and adsorption chiller. The components of the heating system that would be similar for both options have been excluded from analysis (i.e. heating network and its equipment). The functional unit was defined as 1 year of heating and cooling system operation. The system boundaries included selected life cycle stages of facility construction, fuels production, processing and transport, electricity generation and distribution as well as facility operation. A lifespan of 20 years was considered for the facilities. Due to long operation time, it is difficult to foresee the recovery technology that may be used in the future. The recycling and recovery processes are constantly being improved, so the current disposal scenarios can be omitted. Hence, the disposal stage of the facilities was excluded from the life cycle. The functional unit of the LCA study was assumed as 1 year operation.

2.3 Life cycle inventory

The collection of high quality primary data related to the BHC system is essential for the consistency and representativeness of LCA results. Primary data, which were issued empirically from the on-site monitoring of the plant, included: properties of the wood chips used in the biomass boiler; energy consumption during the operation phase; flue gas emissions from the wood chips combustion. The ecoinvent database was furthermore used to collect background data, e.g. concerning equipment manufacture, electricity, and fuels production and transport [13]. No cut-off rules were employed to the background data, because their scope corresponds exclusively to the one set by the ecoinvent datasets.

The first phase of the analyzed scenario is the wood chips production process and its transportation. For modeling this stage, process found in the Ecoinvent 2.2 database was used. In order to evaluate the real woody biomass

characteristics used in the BHC system, a sampling of wood chips from the storage tank of the boiler was carried out. Bulk density, moisture content, ash content, and lower heating value were measured according to CEN/TS 15103, CEN/TS 14774-2, CEN/TS 14775, and CEN/TS 14918. Moisture and ash content was determined using a Thermogravimetric Analyzer TGA-701 LECO. The net calorific value analysis was measured by means of an isoperibolic calorimeter (mod. LECO AC-350). The device gives a gross calorific value of the sample; then the net value is obtained by calculation, from moisture and hydrogen content of the sample. Hydrogen content was evaluated by an elemental analyzer (TruSpec, LECO Co., USA). Finally, bulk density was calculated by the mass material contained in a standard container of 2 L volume.

Primary data on energy consumption of the BHC system during the operation phase were collected by means of direct investigations and a data acquisition system, during the year 2015. In order to provide heating, the biomass boiler was on from January to the end of March and from the end of November to the end of the year, producing about 22.9 MWh. During the cooling period (from mid-June to mid-September), the cooling energy out of the absorption chiller was 13.6 MWh, with a heat of 23.4 MWh from the boiler and a total electric absorption of about 1962 kWh (Table 2). As final remark, a water consumption of about 68 m3, due to the evaporative cooling tower, was noticed in the cooling period.

Table 2. Energy consumption data of the BHC system during the operation phase in 2015

Month Mean outdoor Temperature (°C) Thermal energy Thermal energy to the from boiler (kWh) buildings (kWh) Cooling energy to the building (kWh) Total Electric energy consuption (kWh)

January 7.4 5690 5060 0 98.33

February 7.6 6000 5260 0 127.10

March 11.2 4490 3650 0 111.10

April 15.4 0 0 0 42.10

May 21.0 0 0 0 43.60

June 25.5 1390 0 280 160.00

July 28.3 12010 0 7680 936.30

August 27.3 7770 0 4440 645.90

September 22.3 2230 0 1190 220.30

October 16.1 0 0 0 50.60

November 11.4 1110 1030 0 62.50

December 7.0 8680 7880 0 225.80

Total heating period (1/1-28/3 and 25/11-31/12) - 25970 22880 0 493.20

Total cooling period (15/6-09/09) - 23400 0 13590 1962.5

Chimney emissions from the biomass boiler were investigated adapting the ecoinvent process "Wood chips, from forest, hardwood, burned in furnace 50 kW" to the specific data retrieved during a gas sampling campaign. In particular, CO and NOX emissions were determined by a portable emission analyzer Testo 350 XL. Two hours test was carried out. Furthermore particulate matter sampling was performed under steady state operating conditions. A cascade impactor TCR Tecora (model MSSI) was employed to determine size segregated particulate matter samples. The multistage cascade impactor, designed according to the technical standard UNI EN 23210:2009 for the nozzle dimensioning allows separation into 3 particulate size fractions: >10 ^m (PM>10), between 2.5 and 10 ^m (PM10) and below 2.5 ^m (PM2.5). The particulate matter samples were collected on 47 mm diameter quartz filters conditioned for 48 h before weighting. The gravimetric quantification was carried out with a precision balance (Scaltec SBC 22 model, Scaltec Gmbh, Germany). The efficiency of the biomass boiler was determined under steady-state operation, using the heat loss method [14] by estimating the total losses because of dry flue gas, moisture in the fuel, hydrogen in the fuel, radiation and convection, and partial conversion of C to CO and

subtracting these terms from 100% efficiency. For this estimation the flue gas, the stack temperature, and the fuel feed rate were measured. Finally, according to the Italian law (Legislative Decree no. 152 of 3/4/2006) that prohibits the ash employment for agricultural purpose, landfilling was considered as final disposal. The main information on the inventory phase for the BHC system is reported in Tables 3 and 4.

Table 3. Inventory phase: main aspects for the BHC system scenario (primary data)

Parameters BHC system scenario

Wood composition 50% hardwood, 50% softwood

Wood properties Moisture 25%

Bulk density 241 kg/m3

Ash content 0.65% d.b.

Lower Heating Value 3.92 kWh/kg w.b.

Boiler efficiency 93%

Measured air emissions CO 77.66 mg/Nm3 at 10% O2 content in dry flue gas

NOx 205.14 mg/Nm3 at 10% O2 content in dry flue gas

PM>10 8.92 mg/Nm3 at 10% O2 content in dry flue gas

PM10 13.27 mg/Nm3 at 10% O2 content in dry flue gas

PM2.5 26.05 mg/Nm3 at 10% O2 content in dry flue gas

Table 4. Description of input data for the BHC system LCI per 1 year of operation [13].

Life cycle stage Based on process Amount Source of data

Infrastructure Furnace, wood chips, hardwood 50kW 0.05 p ecoinvent 2.2

Absorption chiller 100kW 0.05 p ecoinvent 2.2

Usage Electricity, low voltage, at grid/IT 2455.7 kWh ecoinvent 2.2

Water, process, well, in ground 68 m3 ecoinvent 2.2

Wood chips, mixed, u=80%, at forest/RER 13.54 ton ecoinvent 2.2

Transport, lorry 20-28 t, fleet average/CH (86 km) 1165 tkm ecoinvent 2.2

Wood chips, from forest, mixed, burned in furnace 50 kW/CH 177,732 MJ ecoinvent 2.2 (modified for CO, NOx, PM emissions)

End-of-life Disposal, wood ash mixture, pure, 0% water, to sanitary landfill/CH 66 kg ecoinvent 2.2

2.4 Reference scenario

The energy and environmental advantages of the BHC system were compared with a conventional heating and cooling system for commercial buildings: an air to air heat pump for cooling (EER, energy efficiency ratio, equal to 3.82) and a natural gas boiler for heating. For this purpose, the modelling phase was carried out using Ecoinvent 2.2 database processes. For heating purposes the process Heat, natural gas, at boiler fan burner non modulating < 100 kW (49,370 kWh/year) was considered, including the fuel input from a low pressure network, infrastructure, emissions, and electricity needed for its operation. For cooling operation, heat pump, 30 kW with an electricity consumption of 3558 kWh/year, obtaining from the above-mentioned cooling energy consumption.

2.5 Impact assessment methodology

Environmental impacts were assessed using 2 midpoint indicators (Cumulative Energy Demand, IPCC 2013 GWP 100 year) and one endpoint indicator (ReCiPe). The Cumulative Energy Demand (CED) is a measure (expressed in MJ) of direct and indirect energy use throughout the entire life cycle of a product or a system. In particular, the category non-renewable fossil was suggested as an indicator for the environmental performance of products and processes [15]. In this study, CED version 1.08 was employed as implemented in Simapro 8.0. The IPCC 2013 GWP 100 year allows to determine the amount of greenhouse gases (in kg CO2eq) emitted in the atmosphere and contributing to global climate change. In its version 1.01, it includes emissions from fossil and

biogenic carbon sources, emissions caused by land use change, and carbon uptake by plants over a 100-year time horizon.

Finally, ReCiPe [16] is one of the most recent impact assessment method that integrates the CML 2000 and the Ecoindicator 99 methods by converting inventory parameters firstly into eighteen midpoint indicators and then into three endpoint damage categories. Midpoint indicators facilitate differentiating between various impact categories and endpoint indicators simplify comparing total damage. Then the three endpoint categories can be aggregated into a single score by assigning appropriate weights. Three weighing sets (hierarchist, egalitarian, and individualist) can be employed, according to three different social perspectives based on the cultural theory of risk. The hierarchist perspective is the ReCiPe's scientific consensus model because unlike the other options it considers common policies over an average timeframe, most frequently 100 years. The aggregated environmental impacts are expressed in Points (Pt). In this paper ReCiPe endpoint version 1.06 with a hierarchic weighting set was assumed.

3. Results and discussion

As mentioned above, ReCiPe method was used to evaluate environmental impacts. This method links midpoint (18 impact categories) and endpoint (3 impact categories and as a single score result) categories. The results for the 18 midpoint indicators can be seen in Table 5.

Table 5. Comparison of the environmental impacts calculated by ReCipe method with a midpoint perspective.

Life cycle category Abbreviations Unit Reference scenario BHC system

Climate change CC kg CO2 eq 9797.2 3102.4

Ozone depletion OD kg CFC-11 eq 6.1E-03 2.6E-04

Human toxicity H.Tox kg 1,4-DB eq 1269.3 3616.5

Photochemical oxidant formation POF kg NMVOC 14.1 40.5

Particulate matter formation PMF kg PM10 eq 5.2 14.0

Ionising radiation IR kg U235 eq 593.9 523.1

Terrestrial acidification TA kg SO2 eq 16.8 29.5

Freshwater eutrophication FE kg P eq 1.1 1.1

Marine eutrophication ME kg N eq 0.6 1.7

Terrestrial ecotoxicity TEcotox kg 1,4-DB eq 0.4 0.8

Freshwater ecotoxicity FEcotox kg 1,4-DB eq 19.1 30.5

Marine ecotoxicity MEcotox kg 1,4-DB eq 22.6 35.3

Agricultural land occupation ALO m2a 23.4 14156.9

Urban land occupation ULO m2a 11.4 212.4

Natural land transformation NLT m2 2.1 2.5

Water depletion WD m3 12.0 19.2

Metal depletion MD kg Fe eq 291.2 582.1

Fossil depletion FD kg oil eq 3649.5 868.5

For the midpoint indicators, BHC system showed better results in five categories (climate change, ozone depletion, ionising radiation, freshwater eutrophication, and fossil depletion), while the reference scenario had better results in thirteen categories (human toxicity, photochemical oxidant formation, particulate matter formation, terrestrial acidification, marine eutrophication, terrestrial ecotoxicity, freshwater ecotoxicity, marine ecotoxicity, agricultural land occupation, urban land occupation, natural land transformation, water depletion, and metal depletion).

In order to highlight the steps that give rise to the main environmental impacts, the phases in the life cycle were grouped into the following macro-categories: infrastructures, use phase-heating, use phase-cooling, auxiliary electricity-heating, auxiliary electricity-cooling. As can be seen from fig. 1, the use phase causes the greatest contributions to the total environmental burdens, mostly due to the NOX emissions from biomass boiler

(photochemical oxidant formation, particulate matter formation, terrestrial acidification, marine eutrophication), and the production of wood chips that causes the occupation of forestry during wood extraction (agricultural land occupation), the construction of new forest roads (natural land transformation) and the emissions from diesel combustion during wood felling and thinning (terrestrial ecotoxicity, fossil depletion).

Fig. 1. Contribution analysis with ReCiPe midpoint method.

As regards the reference scenario, even though they are different categories, the main reason for these results is the electricity consumption of the split-unit for cooling purposes.

For the endpoint results we analyzed at each damage category (human health, ecosystems, and resources) and at the single score result, which combines the aforementioned damage categories into a single unit (Pt). The results can be seen in fig. 2.

soo 700 600 £ 500 400 300 200 100 0

■■■■■

ЩЛ 1

¡■и n

Resources ■ Ecosystems s Human Health

REFERENCE SCENARIO

BHC SYSTEM

Fig. 2. Comparison of the environmental impacts calculated by ReCipe method with an endpoint perspective.

BHC system showed better results for human health and resources, while the reference scenario had better results for ecosystems for the same reasons previously discussed. When these endpoint indicators were normalized and weighted generating a single score result, BHC system had the best results, with a total of 752.9 Pt, while the reference scenario had a total of 940 Pt. The largest impact components are the damages to ecosystems due to agricultural land occupation (48.3%) and damages to resources caused by depletion of fossil fuels (13.8%).

The different environmental performance of the BHC system and the conventional one were even more striking in terms of GWP 100 year footprint. Greenhouse gas emissions for heating and cooling the commercial building (3102 kg CO2eq/year) were over one third of those associated to the reference scenario (9797 kg CO2eq/year).

Finally, the results of comparing the analyzed scenarios with the non-renewable fossil CED indicator confirm the lower environmental impacts of BHC system (36.48 GJ) with respect to those of conventional one (153.3 GJ). The contribution analysis of the BHC system highlighted that auxiliary electricity consumption for cooling production is the phase requiring the most relevant amount of energy (46.9%).

4. Conclusions

In this study, LCA is employed as a method for the assessment of the environmental burden of two different systems for heating and cooling of commercial buildings. Moreover, this paper provides suggestions on the suitability of simplified methods (such as CED and carbon footprinting methods) instead of complex and complete methods (such as the ReCiPe) for process and product life cycle assessment. Results showed the biomass based system is characterized by the best performance with all the applied methods.

For lowering the environmental impact of the BHC system, excluding the possible actions at the biomass production level, attention has to be paid in reducing both the nitrogen oxides emissions from the biomass boiler and the auxiliary electricity consumption of the plant.

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