Carbon Footprint in Building Retrofit

1. Solar Energy: The Ultimate Source

Solar Energy Input

The Earth receives approximately 173,000 terawatts of solar energy continuously
This equals 1.5 × 10¹⁸ kWh/year of solar energy
This is 10,000 times more than global energy consumption

                                    Solar energy received by Earth in one hour could meet global energy needs for an entire year
                                

Distribution of Solar Energy

30% is reflected back to space
47% is absorbed and converted to heat
23% drives the water cycle
Only 0.1% is captured by plants through photosynthesis

Concept: Energy Cascade

All energy forms on Earth ultimately derive from the sun through various transformations

2. Energy, Power, Work, and Heat: Fundamental Concepts

Energy

The capacity to do work, existing in various forms:

Potential energy: Stored energy due to position or state
Kinetic energy: Energy of motion
Thermal energy: Internal energy from molecular motion
Chemical energy: Stored in molecular bonds
Electrical energy: From electric charges

                                    Energy can neither be created nor destroyed, only transformed (First Law of Thermodynamics)
                                

Power

The rate at which energy is transferred or work is done:

Measured in Watts (1 W = 1 Joule/second)
Building applications typically use kilowatts (kW)
Large buildings may have demands in megawatts (MW)

Intuitive Understanding

Power = Energy / Time

A 60W lightbulb uses 60 joules every second

3. Advanced Energy Concepts

Exergy

The maximum useful work obtainable from an energy system:

Measures energy quality and potential usefulness
High-exergy sources: electricity, mechanical energy
Low-exergy sources: waste heat, ambient heat

Matching exergy quality to application increases efficiency

Example: Using low-temperature waste heat for space heating rather than high-quality electricity

Entropy

Measure of energy dispersal and disorder:

Increases in isolated systems (Second Law of Thermodynamics)
Affects energy availability and usefulness
In buildings: thermal mixing, material degradation

Building Entropy

Buildings naturally degrade over time as entropy increases, requiring maintenance and energy inputs to maintain order

Syntropy

The opposite of entropy - organization and complexity creation:

Local decrease in entropy through energy input
Creation of order and organization
In living systems and built environment

Building Application

Retrofitting represents a syntropic process - injecting new order and functionality into existing structures

EMERGY (Embodied Energy)

Total energy consumed in the entire life cycle:

Includes direct and indirect energy inputs
Accounts for energy quality differences
Measured in solar energy equivalents

Building reuse preserves up to 80% of embodied energy compared to new construction

4. Carbon Footprint: Measurement and Scopes

Definition and Units

Carbon footprint measures the total greenhouse gas emissions caused by an activity, expressed as carbon dioxide equivalent (CO₂e):

kg CO₂e: Standard unit for individual products or activities
Tonnes CO₂e: Used for larger scales (buildings, organizations)
kg CO₂e/m²: Normalized by floor area for buildings

Carbon Footprint Scopes

Scope 1: Direct Emissions

On-site combustion (gas boilers, furnaces)
Company vehicles and equipment
Refrigerant leakage

Scope 2: Indirect Energy Emissions

Purchased electricity
District heating and cooling
Purchased steam

Scope 3: Other Indirect Emissions

Embodied carbon in materials
Construction activities
Waste disposal
Occupant transportation
Water supply and treatment

Carbon Footprint in Building Lifecycle

Embodied Carbon

Carbon emissions associated with materials and construction processes:

Material extraction and manufacturing
Transportation
Construction
Maintenance and replacement
End-of-life disposal

Operational Carbon

Carbon emissions from building operation:

Space heating and cooling
Water heating
Lighting
Appliances and equipment
Maintenance activities

Carbon Intensity of Building Materials (kg CO₂e/kg)

Material	kg CO₂e/kg	Notes
Cement	0.8 - 0.9	Portland cement, high intensity from calcination
Steel (virgin)	1.8 - 2.2	Energy-intensive ore processing
Steel (recycled)	0.4 - 0.5	75-80% lower than virgin steel
Aluminum (virgin)	11.0 - 13.0	Very energy-intensive electrolysis
Aluminum (recycled)	0.5 - 1.5	85-95% lower than virgin aluminum
Timber	0.1 - 0.3	Can be carbon negative when sequestration considered

5. The Carbon Case for Building Retrofit

Embodied Carbon Savings

Adaptive reuse preserves embodied carbon in existing structures:

Building reuse saves 50-75% of embodied carbon compared to new construction
Concrete and masonry structures contain significant "sunk carbon"
Historic buildings represent carbon already spent decades or centuries ago

"The greenest building is the one that already exists" - Carl Elefante

Carbon Payback Periods

Time required for operational carbon savings to offset embodied carbon of retrofit:

Simple energy efficiency measures: 1-3 years
Window replacements: 10-30 years
External wall insulation: 5-15 years
Whole building retrofit: 7-20 years

Carbon ROI

Retrofit measures should prioritize highest carbon return on investment

Comparative Carbon Scenarios

CO₂e emissions over 60 years for different building approaches:

40%

60%

New Construction

15%

85%

Basic Retrofit

20%

80%

Deep Retrofit

30%

70%

Net Zero Retrofit

Embodied Carbon Operational Carbon

Tonnes CO₂e

Deep retrofits reduce total lifecycle carbon emissions by 50-70% compared to new construction

6. Practical Carbon Reduction in Building Retrofit

Retrofit Strategies Ranked by Carbon Impact

Fabric-first approach: Insulation, airtightness, window upgrades
Renewable energy systems: Solar PV, heat pumps, solar thermal
Low-carbon materials: Bio-based insulation, mass timber, lime mortars
Smart building controls: Zoning, sensing, demand-responsive systems
Ventilation with heat recovery: MVHR systems with high efficiency

Carbon Intensity of Heating Systems (g CO₂e/kWh)

System Type	g CO₂e/kWh delivered
Direct Electric Heating	208-350 (grid dependent)
Gas Boiler (90% efficient)	215-230
Oil Boiler (85% efficient)	310-330
Air Source Heat Pump (SCOP 2.8)	74-125 (grid dependent)
Ground Source Heat Pump (SCOP 3.5)	59-100 (grid dependent)
Biomass Boiler	20-40 (sustainable sourcing)

Interrelationship of Energy and Carbon

Carbon Intensity Curves

Grid electricity carbon intensity varies by:

Time of day: Lower overnight, higher during peak demand
Season: Lower in summer (more solar), higher in winter
Country: Varies by energy mix (renewable % vs fossil fuels)

Smart retrofits can shift energy demand to low-carbon intensity periods

Carbon Neutral vs. Net Zero

Approach	Definition	Application to Buildings
Carbon Neutral	Balancing emissions with offsets	Purchasing carbon credits to offset remaining emissions
Net Zero Operational Carbon	No net operational emissions	On-site renewables balance operational energy use
Net Zero Embodied Carbon	No net emissions from materials	Carbon sequestering materials balance embodied emissions
Net Zero Whole Life Carbon	No net emissions across lifecycle	Combines operational and embodied approaches

7. Case Studies and Examples

Case Study: Heritage Building Retrofit

Building Type: 19th century brick warehouse

Intervention: Adaptive reuse to office and creative workspace

Carbon Metrics:

Embodied carbon saved by reuse: 1,850 tonnes CO₂e
Embodied carbon of retrofit: 380 tonnes CO₂e
Pre-retrofit operational carbon: 120 tonnes CO₂e/year
Post-retrofit operational carbon: 35 tonnes CO₂e/year
Carbon payback period: 4.5 years

By preserving the structure, 85% of potential demolition and new-build carbon emissions were avoided

Case Study: Modern Building Deep Retrofit

Building Type: 1980s concrete-framed office building

Intervention: Deep energy retrofit and recladding

Carbon Metrics:

Embodied carbon saved by reuse: 2,200 tonnes CO₂e
Embodied carbon of retrofit: 850 tonnes CO₂e
Pre-retrofit operational carbon: 180 tonnes CO₂e/year
Post-retrofit operational carbon: 45 tonnes CO₂e/year
Carbon payback period: 6.3 years

Key Learnings

Modern buildings often have poor envelope performance but good structural systems that can be retained in retrofits

Case Study: Traditional Residential Retrofit (Ireland)

Building Type: 1930s semi-detached house with solid masonry walls

Intervention: Deep retrofit to near-passive standard

Key Measures:

External wall insulation (200mm EPS): U-value improved from 2.1 to 0.15 W/m²K
Triple glazing: U-value improved from 3.5 to 0.8 W/m²K
Air source heat pump replacing oil boiler
MVHR system
3.5 kWp rooftop solar PV

Carbon Results:

Annual carbon reduction: 5.8 tonnes CO₂e (87% reduction)
Embodied carbon of retrofit: 15.2 tonnes CO₂e
Carbon payback: 2.6 years

Case Study: UCC Enterprise Centre

Building Type: 1980s educational building

Intervention: Phased energy retrofit with heritage considerations

Key Measures:

Building envelope upgrading with careful attention to thermal bridging
Heat pump technology replacing gas boilers
Improved glazing while maintaining aesthetic character
Enhanced controls and building management systems

Carbon Results:

51% reduction in operational carbon emissions
Annual carbon savings: approximately 125 tonnes CO₂e
Retained approximately 75% of existing building fabric

Universal Retrofit Carbon Principles

Measure before intervention: Baseline performance assessment and carbon auditing
Maximize structure retention: Preserve embodied carbon in structural elements
Material hierarchies: Prioritize reuse, then recycled, then bio-based, then low-carbon
Energy hierarchies: Reduce demand first, then increase efficiency, then add renewables
Futureproofing: Design for adaptability, disassembly, and further carbon reductions

Building retrofit design should consider both immediate carbon impact and long-term lifecycle emissions