Feasibility of Planting Trees around Buildings as a Nature-Based Solution of Carbon Sequestration—An LCA Approach Using Two Case Studies
Abstract
:1. Introduction
2. Literature Review
2.1. Keyword Search in Databases
- Real case studies, with details about design solutions, materials, energy consumption, and energy sources;
- Results about life cycle carbon balance, based on LCA calculations;
- Methods, software tools, and databases used for the assessment of carbon emission;
- The carbon sequestration potential of vegetation applied to the building context;
- The estimation of annual carbon sequestration rates of trees and vegetation.
- An assessment of the positive impacts of planting urban trees near buildings as a nature-based solution to offset buildings’ life cycle embodied and operational GHG emissions, by considering direct carbon sequestration potential;
- A discussion of the quality and completeness of whole building life cycle carbon analysis, with applications for real case studies.
2.2. Low-Carbon Design and Vegetation
2.3. Life Cycle Assessment in Canadian Context
3. Materials and Methods
3.1. Overview
3.2. Estimation of Building’s Environmental Impacts
3.3. Carbon Sequestration Potential of Urban Trees
3.4. Case Study 1: Future Buildings Laboratory
3.5. Case Study 2: Single-Detached House
4. Results and Discussion
4.1. LCA Results: Future Buildings Laboratory
- Although the operational emissions (module B6) are only dependent on two inputs (building location and annual energy consumption by type of fuel), the result provided by Athena for this module (9737 kgCO2eq) is almost 80% higher than the results from One Click LCA (5445 kgCO2eq). The reason is that Athena contains highly specific data for North American regions, which means that city-level geographic relevance is critical, especially for operational emissions. According to Athena’s Transparency Document [68] and customer support service, starting with version v.5.4, the source data for electricity profiles for Canadian provinces has been changed to Ecoinvent 3.4-2017, which is very likely to include factors for biogenic decay in hydro reservoirs (rotting vegetation emitting CO2 and methane (CH4)), and other impacts related to transmission processes, which results in a multiplier factor of 0.018302 kgCO2eq per kWh. For One Click LCA, the operational electricity use emissions are calculated considering a factor of 0.010234 kgCO2eq per kWh of electricity. Based on the information presented from reading data-cards available in the One Click LCA browser, the calculation is done according to an internally verified LCA study for country-specific electricity mixes (Quebec/Canada) based on the International Energy Agency (IEA) and Ecoinvent databases from 2020.
- There is a high environmental impact due to the use of Extruded Polystyrene (XPS) insulation materials, which is the type of insulation specified for the FBL’s foundation and roof. The impact of XPS exceeds any other materials, carrying a GWP of around 20,700 kgCO2eq, which represents 25% of the total life cycle emissions for the baseline scenario (modules A to C). Both softwares use data from publicly available Environmental Product Declarations (EPDs) from Owens Corning and Dupont to estimate life cycle CO2eq emissions impacts. The raw material extraction and manufacturing processes of XPS are the highest contributing modules, including emissions from electricity, natural gas and liquefied petroleum gas combustion, as well as blowing agent emissions from the trimming, cutting, and profiling of the XPS boards. The chart presented in Figure 7 adapted from One Click LCA to demonstrate the total GWP contribution related to the most impactful materials considered in this case study.
- 3.
- The life cycle stage “replacement; refurbishment” (modules B4 and B5) also represents a relevant burden on the final LCA results. It contributes around 14,300 kgCO2eq, representing 17% of the FBL’s emissions, calculated using both softwares. The service life determines how long the product is in use before it is replaced. Foundation materials, for example, are never replaced. Insulation materials usually have a service life of 75 years, as defined in different EPDs, which is longer than the 60-years’ service life assumed for the case studies in this paper. Equipment such as HVAC and PV have a shorter service life (20 to 25 year); taking the PVs as example, it carries embodied emission of around 3000 kgCO2eq due to manufacturing processes (A1–A5), and 6000 kgCO2eq more due to two events of replacement (at building age of 20 years and 40 years).
- 4.
- Default scenarios are assumed for End-of-Life stages. The default inputs are based on the processing chain defined in EPDs, or local common practice. In One Click LCA, it is possible to alternate those scenarios that impact the results for modules C2 to C4, and also for module D, if applicable. Examples of end-of-life treatments are landfill (for inert materials), wood incineration, plastic-based material incineration, steel recycling, gypsum recycling, and glass-containing and metal-containing product recycling.
4.2. LCA Results: Single-Detached House
4.3. Final Balance: Potential for Carbon Sequestration Using Urban Trees
4.4. Aditional Scenarios and Directions for Future Work
5. Conclusions
Author Contributions
Funding
Conflicts of Interest
References
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Modules | Life Cycle Stages | Included |
---|---|---|
A1–A3 | Raw material supply; Transport; Manufacturing | ✔ |
A4 | Transport from manufacturing plant to construction site | ✔ |
A5 | Construction–installation process (equipment energy use) | ✔ |
B1 | Installed product in use | |
B2 | Maintenance | |
B3 | Repair 1 | ✔ |
B4–B5 | Replacement; Refurbishment (according to materials’ service life) | ✔ |
B6 | Operational energy use | ✔ |
B7 | Operational water use | |
C1–C4 | De-construction/demolition; Transport; Waste Processing; Disposal | ✔ |
D | Benefits beyond building life (biogenic carbon in wood products) 2 | ✔ |
Building Elements | U-Value |
---|---|
Slab-on-grade foundations | 0.13 |
Exterior walls | 0.22 |
Roof | 0.14 |
Windows | 1.30 |
Doors | 1.40 |
Inputs | Value | Unit |
---|---|---|
Occupancy | 20.0 | m2/person |
Lighting power density | 5.0 | W/m2 |
Appliances and plug loads | 8.0 | W/m2 |
Heating setpoint | 22.0 | °C |
Heating setback | 18.0 | °C |
Cooling setpoint | 23.0 | °C |
Coefficient of performance (summer) | 3.5 | - |
Coefficient of performance (winter) | 2.0 | - |
Ventilation rate (per person) | 5.0 | L/sec/person |
Ventilation rate (per area) | 0.9 | L/sec/m2 |
Air change rate (per hour, at 50 Pa) | 0.8 | ACH |
Project Specification | One Click LCA | Athena | ||
---|---|---|---|---|
m3 | 26.04 | Concrete 30 MPa—15 cm slab + borders | Ready-mix concrete, 30 Mpa Industry Average Benchmark (CRMCA) | Concrete Benchmark CAN 30 MPa |
kg | 1953.6 | Steel bars (mesh) d = 10 mm, 10 × 10 cm | Reinforcement steel (rebar), 7850 kg/m3 (Gerdau, Whitby plant) | Rebar, Rod, Light Sections |
m2 | 198.40 | Insulation, RSI-3.42, rigid, XPS, 127 mm | XPS insulation, 15 psi, R-10, 50.8 mm, Foamular XPS (Owens Corning) | Extruded Polystyrene |
m2 | 156.75 | Insulation, RSI-2.59, rigid, XPS, 76 mm | ||
m2 | 197.90 | Insulation, RSI-4.29 cavity fill, FG, 140 mm | Glass wool insulation panels, unfaced, generic, L = 0.031 W/mK, R = 3.23 m2 K/W | FG LF Cavity Fill R22 |
m2 | 197.90 | Insulation, RSI-1.41, semi-rigid, MW, 51 mm | Rock wool insulation board, R = 8.6, 50.8 mm, 88 kg/m2, (Rockboard 60) | MW Batt R11-15 |
m2 | 119.22 | Insulation, RSI-1.41, semi-rigid, MW, 89 mm | ||
m2 | 156.75 | Insulation, RSI-5.64, semi-rigid, MW, 235 mm | Mineral fiber batt insulation, 6.89 in | MW Batt R30 |
m2 | 124.10 | Gypsum board, fire resistant, 13 mm | Glass-mat gypsum boards, fire/moisture., 12.7 mm, 10.15 kg/m2 (AGC) | 1/2″ Fire- Type X Gypsum Board |
m2 | 395.19 | Gypsum board, regular, 13 mm | Gypsum plaster board, regular, generic, 6.5–25 mm, 10.725 kg/m2 for 12.5 mm | 1/2″ Regular Gypsum Board |
m2 | 400.89 | Gypsum board, fiber-board, 16 mm | Gypsum plaster board, regular, generic, 6.5–25 mm, 10.725 kg/m2 for 12.5 mm | 5/8″ Gypsum Fibre Gypsum Board |
m2 | 197.90 | Plywood board, 13 mm | Softwood plywood, 477.33 kg/m3 (Canadian Wood Council) | Softwood Plywood |
m2 | 156.75 | Plywood board, external, 19 mm | Softwood plywood, 709.79 kg/m3 (American/Can. Wood Council) | |
m2 | 23.12 | Plywood board, 19 mm | Softwood plywood, 477.33 kg/m3 (Canadian Wood Council) | |
m3 | 16.33 | Glued Laminated Timber | Glue laminated timber (Glulam), 467.3 kg/m3 (Canadian Wood Council) | GluLam Sections |
m3 | 8.16 | Wood joists, glulam, 5 × 25 cm, 300 mm sp | I-joist, wood (FPInnovations) | |
m3 | 1.34 | Wood joints cover for cladding, 2 × 4 cm | Softwood lumber, kiln-dried, 19 mm, 460 kg/m3 (Can. Wood Council) | Small Dim. Softwood Lumb, kiln-dried |
m3 | 6.84 | Wood studs, 5 × 20 cm, 400 mm spacing | ||
m2 | 197.90 | Eastern cedar cladding, painted, 19 mm | Western red cedar bevel siding, painted, 1 × 6 in (W Red Cedar Lumber Assoc.) | Cedar Wood Shiplap Siding |
m2 | 532.34 | Air/water barrier 6 mil | Air and water barrier system, mechanically fastened, 0.11 kg/m2, Tyvek (DuPont) | Air Barrier |
m2 | 396.65 | Vapor barrier, dynamic, 6 mil | Polypropylene Scrim Kraft Vap. Ret. Cl | |
m2 | 156.75 | Metal roofing syst (45 mm w/membrane) | Hot-dip galvanized steel sheets, 0.4–3.0 mm, zinc coating, 0.28 kg/m2 | Metal Roof Cladding—Resident. 30 Ga |
m2 | 156.75 | Impermeable membrane (roof) | SPPR PVC roofing membrane, single-ply, 40 mil (Chemic.Fab. Film Assoc.) | #30 Organic Felt |
kg | 200.00 | Bolts, Fasteners, Clips | Structural steel profiles, generic, 40% recycled content | Bolts, Fasteners, Clips |
m2 | 26.00 | Windows aluminum frame | Aluminum frame windows, 37 kg/m2—30% Alum., 61% Glazing (AluQuébec) | Aluminum Window Frame |
m2 | 26.00 | Double Glazed Hard Coated Argon | Double Glazed Hard Coated Argon | |
m3 | 0.20 | Doors/steel doors | Galvanized steel door w/ polystyrene, 44.5 mm, 41 kg/unit (De La Fontaine) | Rough Lumber SFWP |
m | 75.00 | Steel structure on roof to support BIPV/T | Stainless steel crash rails with tube brackets, 10.84 kg/m (Constr.Specialties) | Steel Tubing |
m2 | 120.00 | Industrial floor paint—Epoxy or similar | Water-based epoxy floor and wall coating, 2.31 kg/m2 (SherWilliams) | Solvent Based Alkyd Paint |
Solvent Based Varnish | ||||
m2 | 698.31 | Paint intern | Recycled latex paints, interior, 12 m2/L, 1.23 kg/L, 0.205 kg/m2, (Laurentide) | Water Based Latex Paint |
m2 | 23.12 | Vinyl cover, 12pprox. 3 mm | Vinyl tile flooring, 2.4–3.2 mm, 6.4–6.9 kg/m2 (Armstrong, Tarkett) | Vinyl Siding |
unit | 1.00 | HVAC (air src heat pump, 2.5 kW output, 47.5 MJ/h) + air handling unit | Ground source heat pump (excluding ground tubes), per 1 kW max output | N/A—One Click’s results adopted |
Air hand. Unit, w/ heat recovery, indirect liq. Circulation, 1000 m3/h, 92 kg/unit | N/A—One Click’s results adopted | |||
m2 | 15.00 | PV system 1.63 kWp (BIPV on south façade) | PV polycrystalline panel, per m2, 14.5 kg/m2, 210 Wp (One Click LCA) | N/A—One Click’s results adopted |
Energy Simulation Inputs | Value | Unit | Envelope Assemblies | U-Value (W/m2.K) |
---|---|---|---|---|
Occupancy | 60.0 | m2/person | Basement floor | 1.00 |
Temperature setpoint for heating | 19.0 | °C | Basement walls | 0.48 |
Temperature domestic hot water | 55.0 | °C | Above ground walls | 0.45 |
Forced-air natural gas furnace heating | 80 | MJ/h | Roof and ceiling | 0.18 |
Volumetric air flow rate | 210.0 | L/s | ||
Air change rate (measured, at 50 Pa) | 7.76 | ACH |
Project Specification | One Click LCA | Athena | ||
---|---|---|---|---|
m3 | 36.77 | Concrete 30 Mpa | Ready-mix concrete, 30 MPa Industry Average Benchmark (CRMCA) | Concrete Benchmark CAN 30 MPa |
kg | 3991.24 | Steel rebars (double mesh) | Reinforcement steel (rebar), generic, 80% recycled content, A615 | Rebar, Rod, Light Sections |
m3 | 12.55 | Brick veneer, 10.9 mm thickness | Clay brick, 2120 kg/m3 (several manufacturers) | Ontario (Standard) Brick |
m3 | 3.46 | Mortar (0.03 3 per m2 of brickwork) | Lightweight mortar, single component, 3.625 kg/m2 (Mapei) | Mortar |
m2 | 107.62 | Insulation RSI-4.94, FG, cavity fill, 89 mm | Insulation, glass wool, loose, 30 m2 K/W, Industry average US (NAIMA) | FG LF Cavity Fill R30 |
m2 | 137.55 | Insulation RSI-3.53, FG, cavity fill, 152 mm | Glass wool insulation panels, unfaced, generic, L = 0.031 W/mK, R = 3.23 m2 K/W | FG LF Open Blow R13-20 |
m2 | 137.55 | Insulation RSI-3.53 FG, continuous, 152 mm | ||
m2 | 958.57 | Gypsum board, 13 mm | Gypsum plaster board, regular, generic, 12.5 mm, 10.725 kg/m2 | 1/2” Regular Gypsum Board |
m2 | 594.63 | Plywood board, 13 mm | Softwood plywood, 477.33 kg/m3 (Canadian Wood Council) | Softwood Plywood |
m2 | 497.88 | Polyethylene sheet, 6 mil | PVC-polyester waterproofing membrane (Chemical Fabrics and Film Association) | 6 mil Polyethylene |
m2 | 275.10 | Wood flooring | Solid hardwood flooring, 19 mm, 12.35 kg/m2 (Wickham) | Spruce Wood tongue/groove (closest option) |
m3 | 6.88 | Wood studs 5 × 15 cm | Softwood lumber, kiln-dried, 460 kg/m3, (Canadian Wood Council) | Small Dimension Softwood Lumber, kiln-dried |
m3 | 8.80 | Wood studs 5 × 10 cm | ||
m3 | 1.70 | Wood joists 5 × 10 cm | GluLam Sections | |
m3 | 0.76 | Wood Doors | Hardwood lumber (Quebec Wood Export Bureau) | Rough Lumber SFWP |
m2 | 17.00 | Windows aluminum frame | Aluminum frame windows, 37 kg/m2, 30% Alum., 61% Glazing (AluQuébec) | Aluminum Window Frame |
m2 | 17.00 | Double glazed units | Double Glazed Soft Coated Air | |
m2 | 958.56 | Paint intern | Recycled latex paints, interior, colored, 0.205 kg/m2 (Laurentide re/sources) | Water Based Latex Paint |
m2 | 204.36 | Asphalt shingle | Fiberglass asphalt shingle roofing system, 12.7 kg/m2 (ARMA) | Organic Felt shingles 30 yr |
m2 | 204.36 | Organic felt | SPPR PVC roofing membrane, 60 mil (Chemical Fabrics and Film Association) | 6 mil Polyethylene |
kg | 200.00 | Bolts, Fasteners, Clips | Structural steel profiles, generic, 40% recycled content, I, H, U, L, and T sections | Bolts, Fasteners, Clips |
unit | 1.00 | HVAC (forced-air nat gas furnace, 80 MJ/h) | Air handling unit, w/ heat recovery, liquid circulation, 1000 m3/h, 92 kg/unit | N/A—One Click results adopted |
Modules | Life Cycle Stages | One Click LCA kgCO2eq over 60 yr | Athena kgCO2eq over 60 yr |
---|---|---|---|
A1–A3 | Material manufacturing processes | 55,715.76 | 51,692.01 |
A4 | Transportation to site | 2131.45 | 1793.95 |
A5 | Construction process | 2633.84 | 1647.87 |
B4–B5 | Replacement; Refurbishment | 14,282.14 | 14,320.24 |
B6 | Operational energy use | 5445.38 | 9737.97 |
C1–C4 | End-of-life (demolition; disposal; waste processing) | 3313.14 | 3473.99 |
D | Benefits beyond building’s life (biogenic carbon in wood products) | −35,885.45 | −27,553.12 |
Scenario 1 | Total Emissions—Modules A to C—baseline scenario | 83,521.71 (11.13) | 82,666.02 (11.02) |
Scenario 2 | Total Emissions—Modules A to D | 47,636.26 (6.31) | 55,112.90 (7.34) |
Obs. 1: HVAC and PV are not available in Athena database. Thus, for these two items, the values from One Click were considered for Athena; Obs. 2: Values between parenthesis (e.g., (9,28)) refers to the equivalent CO2eq emissions results per m2 of heated floor area per year. |
Modules | Life Cycle Stages | One Click LCA kgCO2eq over 60yr | Athena kgCO2eq over 60yr |
---|---|---|---|
A1–A3 | Material manufacturing processes | 36,404.74 | 28,419.32 |
A4 | Transportation to site | 2845.62 | 2142.13 |
A5 | Construction process | 1968.34 | 1213.91 |
B4–B5 | Replacement; Refurbishment | 9812.94 | 9378.59 |
B6 | Operational energy use | 491,894/29,443 * | 523,812/52,654 * |
C1–C4 | End-of-life (demolition; disposal; waste processing) | 1981.08 | 1889.72 |
D | Benefits beyond building life (biogenic carbon in wood products) | −26,084.30 | −25,736.74 |
Scenario 1 | Total Emissions (Modules A to C)—baseline scenario | 544,907.34 (35.20) | 566,856.35 (36.62) |
Scenario 2 | Total Emissions (Modules A to D) | 518,823.04 (33.51) | 541,119.61 (34.95) |
Scenario 3 | Total Emissions (Modules A to C)—natural gas converted to electricity | 82,456.32 (5.32) | 95,697.69 (6.18) |
* Emissions from module B6 (operational energy use) considering the setup where natural gas was converted to electricity. Obs. 1: HVAC and Boiler are not available in Athena’s database. Thus, for these two items, the values from One Click LCA were considered for Athena; Obs. 2: Values between parenthesis (e.g., (35.20)) refers to the equivalent CO2eq emissions results per m2 of heated floor area per year. |
REAL SCENARIO 1 (electricity + natural gas) | Energy Consumption (Annual) | One Click LCA kgCO2eq over 60yr | Athena kgCO2eq over 60yr |
---|---|---|---|
Electricity | 9725 kWh/year | 5971 | 10,679 |
Natural gas | 3561.3 m3/year | 485,923 | 513,133 |
Total Operational Emissions (module B6) | 491,894 | 523,812 | |
SCENARIO 3 (natural gas converted to electricity) | |||
Electricity | 9725 kWh/year | 5971 | 10,679 |
Electricity (from natural gas) | 38,225 kWh/year | 23,472 | 41,975 |
Total Operational Emissions (module B6) | 29,443 | 52,654 | |
Obs. 1: 13 of natural gas is equivalent to 10.7330 kW [67] Obs. 2: Equivalent CO2 emissions per kWh from electricity: 0.010234 kgCO2eq/kWh (One Click) and 0.018302 kgCO2eq/kWh (Athena) Obs. 3: Equivalent CO2 emissions per kWh from natural gas: 0.211869 kgCO2eq/kWh (One Click) and 0.223734 kgCO2eq/kWh (Athena) |
Total Emissions (without trees) kgCO2eq over 60yr | Total CO2 Sequestration * kgCO2eq | Final Carbon Balance (with trees) kgCO2eq over 60yr | Trees Contribution [%] | |||||
---|---|---|---|---|---|---|---|---|
OneClick | Athena | per year | over 60y | One Click | Athena | One Click | Athena | |
FUTURE BUILDINGS LAB | ||||||||
Scenario 01 (A to C)-baseline | 83,522 | 67,531 | 235.7 | 14,145 | 69,377 | 68,521 | 16.9% | 17.1% |
Scenario 02 (A to D) | 47,636 | 39,977 | 33,491 | 40,968 | 29.7% | 25.7% | ||
SINGLE-DETACHED HOUSE | ||||||||
Scenario 01 (A to C)-baseline | 544,907 | 566,856 | 290.3 | 17,418 | 527,489 | 549,438 | 3.2% | 3.1% |
Scenario 02 (A to D) | 518,823 | 541,120 | 501,405 | 523,702 | 3.4% | 3.2% | ||
Scenario 03 (A to C) - gas-free | 82,456 | 95,698 | 65,038 | 78,280 | 21.1% | 18.2% | ||
* Calculated using annual CO2 sequestration rate of 0.575 kgCO2eq/m2TC, garden areas of 410 m2 (FBL) and 505 m2 (Single-detached house), and 60-year time horizon. |
Operational Emissions (Module B6) kgCO2eq over 60yr | Total CO2 Sequestration kgCO2eq over 60yr | Carbon Balance (Operational Stage) net kgCO2eq | Trees Contribution [%] | ||||
---|---|---|---|---|---|---|---|
One Click | Athena | From Trees | One Click | Athena | One Click | Athena | |
Future Buildings Laboratory | 5445 | 9737 | 14,145 | −8700 | −4408 | 260% | 145% |
Single-detached House * | 29,443 | 52,654 | 17,418 | 12,025 | 35,236 | 59% | 33% |
* Considering the scenario where natural gas has been converted to energy equivalent value of electricity. |
Benefits beyond building’s life (Biogenic carbon in wood products) | 35,885 |
Garden fully covered by urban trees | 14,145 |
1.63 kWp vertical PVs system electricity generation | 875 |
130 m2 irrigated and fertilized green roof * | 33,540 |
Total emissions offset | 84,445 |
Final balance with addition solutions: ** 83,522 – 84,445 = – 893 | |
* For the green roof, a 10y calculation period was assumed, since this kind of vegetation may have a shorter life cycle. ** See Table 7. |
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© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
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Grossi, F.; Ge, H.; Zmeureanu, R.; Baba, F. Feasibility of Planting Trees around Buildings as a Nature-Based Solution of Carbon Sequestration—An LCA Approach Using Two Case Studies. Buildings 2023, 13, 41. https://doi.org/10.3390/buildings13010041
Grossi F, Ge H, Zmeureanu R, Baba F. Feasibility of Planting Trees around Buildings as a Nature-Based Solution of Carbon Sequestration—An LCA Approach Using Two Case Studies. Buildings. 2023; 13(1):41. https://doi.org/10.3390/buildings13010041
Chicago/Turabian StyleGrossi, Felipe, Hua Ge, Radu Zmeureanu, and Fuad Baba. 2023. "Feasibility of Planting Trees around Buildings as a Nature-Based Solution of Carbon Sequestration—An LCA Approach Using Two Case Studies" Buildings 13, no. 1: 41. https://doi.org/10.3390/buildings13010041