BREEAM In Use Energy Calculator

Assess and improve the energy performance of your existing buildings using BREEAM In Use principles.

BREEAM In Use Energy Calculation

Your Building Energy Performance

— kWh/m²/year

Calculation Method:
1. Total Annual Energy Use (kWh): Sum of heating, cooling, lighting, and other energy uses.
`Total Energy = Heating + Cooling + Lighting + Other`
2. Energy Use Intensity (EUI) (kWh/m²/year): Total annual energy use divided by the Gross Internal Floor Area.
`EUI = Total Energy / Building Area`
3. Occupancy Load Factor: A measure representing energy use per occupied hour, calculated as Total Energy Use divided by the product of Occupancy Hours Per Week and 52 weeks per year. This helps normalize for operational intensity.
`Occupancy Load Factor = Total Energy / (Occupancy Hours Per Week * 52)`

Annual Energy Consumption Breakdown

Energy Use by Category (kWh/year)

Energy Category	Input Value (kWh)	Percentage of Total
Heating	—	–%
Cooling	—	–%
Lighting	—	–%
Other (Appliances, etc.)	—	–%
Total	—	100%

Energy Performance Over Time (Simulated)

What is BREEAM In Use Energy?

BREEAM In Use (Building Research Establishment Environmental Assessment Method) is a globally recognized sustainability assessment method for existing buildings. The ‘In Use’ part specifically focuses on how a building performs once it is occupied and operational. The BREEAM In Use energy calculator component is crucial for understanding and quantifying a building’s energy consumption. It provides a framework to measure energy performance, identify areas for improvement, and benchmark against industry standards. This assessment helps building owners and managers demonstrate their commitment to sustainability, reduce operational costs, and enhance the market value of their properties.

Who should use it: Building owners, facility managers, asset managers, sustainability consultants, and anyone responsible for the operation and performance of existing commercial, industrial, or institutional buildings. It’s particularly valuable for those seeking to achieve BREEAM certification or improve their building’s environmental credentials.

Common misconceptions: A common misconception is that BREEAM In Use energy assessment is solely about the building’s fabric (insulation, windows). While important, it heavily emphasizes operational energy use – how the building is used, managed, and the efficiency of its systems (heating, cooling, lighting, equipment). Another misconception is that it’s a one-time assessment; BREEAM In Use encourages continuous monitoring and improvement to maintain and enhance energy performance over time.

BREEAM In Use Energy Formula and Mathematical Explanation

The core of the BREEAM In Use energy assessment lies in calculating the building’s Energy Performance Ratio (EPR) and Energy Use Intensity (EUI). Our simplified calculator focuses on deriving the EUI and providing key intermediate values.

Key Calculations:

1. Total Annual Energy Use (kWh): This is the sum of all energy consumed by the building over a year, including heating, cooling, lighting, and power for appliances and equipment.

   Total Energy Use = Eheating + Ecooling + Elighting + Eother

2. Energy Use Intensity (EUI) (kWh/m²/year): This metric normalizes the total energy consumption by the building’s floor area, allowing for comparison between different sized buildings. It represents the average energy consumed per square meter per year.

   EUI = Total Energy Use / Gross Internal Floor Area (GIA)

3. Occupancy Load Factor: This calculation helps to understand energy use in relation to how much the building is used. It normalizes energy use by weekly operating hours.

   Occupancy Load Factor = Total Energy Use / (Weekly Operating Hours × 52 weeks)

Variables Table:

BREEAM In Use Energy Calculator Variables

Variable	Meaning	Unit	Typical Range / Notes
Gross Internal Floor Area (GIA)	Total usable floor space within the building envelope.	m²	e.g., 100 – 50,000+
Weekly Operating Hours	Average hours the building is occupied and operational per week.	hours/week	e.g., 20 (part-time) – 60 (24/7 operation)
Annual Heating Energy Use	Energy consumed by the heating system annually.	kWh	Varies greatly by climate, building age, and insulation.
Annual Cooling Energy Use	Energy consumed by the cooling/air conditioning system annually.	kWh	Varies by climate, building use, and internal gains.
Annual Lighting Energy Use	Energy consumed by internal and external lighting systems annually.	kWh	Depends on lighting type, controls, and occupancy.
Annual Other Energy Use	Energy consumed by equipment, appliances, IT, lifts, etc.	kWh	Significant in office and data center environments.
Total Annual Energy Use	Sum of all energy categories.	kWh	Indicator of overall building energy demand.
Energy Use Intensity (EUI)	Normalized energy consumption per unit area.	kWh/m²/year	Benchmark metric. Lower is better. See BREEAM benchmarks.
Occupancy Load Factor	Energy use normalized by operational hours.	kWh/hour	Helps compare efficiency relative to usage intensity.

Understanding these variables allows for a precise calculation of your building’s energy performance, a key step in any sustainability assessment.

Practical Examples (Real-World Use Cases)

Example 1: Modern Office Building

Scenario: A 5-story office building in a temperate climate, used 5 days a week, 9 hours a day.

Inputs:

• Gross Internal Floor Area (GIA): 10,000 m²
• Weekly Operating Hours: 45 hours
• Annual Heating Energy Use: 70,000 kWh
• Annual Cooling Energy Use: 30,000 kWh
• Annual Lighting Energy Use: 40,000 kWh
• Annual Other Energy Use (IT, appliances): 80,000 kWh

Calculations:

• Total Annual Energy Use = 70,000 + 30,000 + 40,000 + 80,000 = 220,000 kWh
• EUI = 220,000 kWh / 10,000 m² = 22 kWh/m²/year
• Occupancy Load Factor = 220,000 kWh / (45 hours/week * 52 weeks) = 114.58 kWh/hour

Interpretation:

An EUI of 22 kWh/m²/year is generally considered good for a modern office building, indicating efficient operations. The occupancy load factor of 114.58 kWh/hour provides context for energy use relative to its operating schedule. Further benchmarking against similar buildings would be advised.

Example 2: Older Retail Unit

Scenario: A single-level retail space in a warmer climate, open 7 days a week, 10 hours a day.

Inputs:

• Gross Internal Floor Area (GIA): 1,500 m²
• Weekly Operating Hours: 70 hours
• Annual Heating Energy Use: 15,000 kWh (minimal heating needed)
• Annual Cooling Energy Use: 60,000 kWh (significant due to climate & equipment)
• Annual Lighting Energy Use: 25,000 kWh
• Annual Other Energy Use (POS, refrigeration, equipment): 45,000 kWh

Calculations:

• Total Annual Energy Use = 15,000 + 60,000 + 25,000 + 45,000 = 145,000 kWh
• EUI = 145,000 kWh / 1,500 m² = 96.67 kWh/m²/year
• Occupancy Load Factor = 145,000 kWh / (70 hours/week * 52 weeks) = 39.73 kWh/hour

Interpretation:

An EUI of 96.67 kWh/m²/year for a retail unit, especially in a warm climate with high cooling demand, might be within typical ranges but warrants investigation. The high proportion of cooling energy suggests potential opportunities for improvement through measures like enhanced insulation, better HVAC controls, or efficient refrigeration. This EUI would likely indicate a lower building performance score within BREEAM In Use.

How to Use This BREEAM In Use Energy Calculator

1. Input Building Data:
   • Enter the Gross Internal Floor Area (GIA) in square meters.
   • Specify the Weekly Operating Hours the building is typically in use.
   • Input the Annual Energy Consumption for Heating, Cooling, Lighting, and Other (appliances, equipment) in kilowatt-hours (kWh). These figures should ideally come from utility bills or sub-metering data.
2. Calculate: Click the “Calculate Energy Use” button. The calculator will process your inputs instantly.
3. Understand the Results:
   • Primary Result (Highlighted): Your building’s Energy Use Intensity (EUI) in kWh/m²/year. This is the key metric for overall energy efficiency per unit area.
   • Total Annual Energy Use: The total energy consumed by the building annually.
   • Energy Use Intensity (EUI): The normalized metric showing energy per square meter.
   • Occupancy Load Factor: Energy use normalized by operational hours, indicating intensity.
4. Analyze the Breakdown: Review the table showing the percentage contribution of each energy category (heating, cooling, lighting, other) to the total consumption. This helps pinpoint where the most energy is being used.
5. Interpret the Chart: The chart provides a visual comparison, often contrasting your building’s EUI with a relevant benchmark (e.g., BREEAM recommendations for similar building types).
6. Decision-Making:
   • High EUI: Indicates potential for significant energy savings. Focus on the largest energy consuming categories identified in the table.
   • High Occupancy Load Factor relative to EUI: May suggest inefficiencies during operating hours.
   • Use the results to identify target areas for energy efficiency improvements, such as upgrading lighting, improving HVAC controls, or enhancing insulation. Compare your results to BREEAM benchmarks to understand your building’s relative performance.
7. Reset & Recalculate: Use the “Reset” button to clear inputs and try different scenarios or correct errors.
8. Copy Results: Use the “Copy Results” button to save or share your calculated figures and assumptions.

This tool provides a foundational understanding, aiding decisions for better building management strategies.

Key Factors That Affect BREEAM In Use Energy Results

Several factors significantly influence a building’s energy performance as measured by BREEAM In Use. Understanding these is crucial for accurate assessment and effective improvement strategies:

• Building Age and Construction Quality: Older buildings often have poorer insulation, less efficient windows, and outdated HVAC systems, leading to higher energy use compared to modern, well-insulated structures. The quality of construction and any subsequent retrofits play a vital role.
• Climate and Weather Conditions: External temperatures, solar radiation, and humidity directly impact heating and cooling loads. Buildings in extreme climates will naturally consume more energy for thermal comfort control than those in moderate climates. Energy modeling can help predict these impacts.
• Building Services Systems (HVAC & Lighting): The efficiency, design, maintenance, and control strategies of Heating, Ventilation, and Air Conditioning (HVAC) systems and lighting are paramount. Inefficient, poorly maintained, or improperly controlled systems can dramatically inflate energy consumption. Use of LED lighting and smart controls significantly reduces lighting energy.
• Occupancy Patterns and Usage: How a building is used – the number of occupants, their activities, operating hours, and equipment usage (e.g., IT, machinery) – directly drives energy demand, particularly for lighting, cooling (from occupants and equipment), and “other” energy categories. Higher occupancy and intensive equipment use generally increase energy consumption.
• Building Management Systems (BMS) & Controls: Advanced BMS can optimize HVAC and lighting schedules, respond to real-time conditions, and monitor energy use. Poorly configured or absent controls lead to energy waste, such as heating and cooling operating simultaneously or lights left on in unoccupied areas.
• Energy Procurement and Tariffs: While not directly impacting physical energy use, the type of energy contract and tariffs can influence the financial cost of energy consumption. However, BREEAM In Use primarily focuses on *consumption* (kWh), not cost, though cost reduction is a key outcome of improving performance.
• Renewable Energy Generation: On-site generation (e.g., solar PV) reduces the net energy imported from the grid. While BREEAM In Use focuses on consumption, net energy consumption figures are often considered, and the potential for renewable integration is a factor in overall sustainability.
• Inflation and Energy Price Fluctuations: While not directly part of the kWh calculation, future energy price expectations influence the financial viability of efficiency investments. Higher projected costs make efficiency measures more attractive.
• Maintenance and Operational Practices: Regular maintenance of building systems (e.g., HVAC servicing, filter changes) and adherence to energy-efficient operational practices by staff are critical for sustained performance. Neglect leads to gradual degradation of efficiency.

Addressing these factors systematically is key to achieving better building sustainability ratings.

Frequently Asked Questions (FAQ)

What is the primary output of the BREEAM In Use energy calculator?

The primary output is the Energy Use Intensity (EUI) in kWh/m²/year. This metric normalizes energy consumption by floor area, providing a key indicator of the building’s energy efficiency.

Where can I find the data for annual energy consumption?

This data can typically be found on your building’s utility bills (electricity, gas, etc.) for the past year. For more accurate results, sub-metering for specific systems (like lighting or HVAC) or a Building Management System (BMS) log can provide detailed consumption figures.

How does BREEAM In Use relate to new build assessments?

BREEAM In Use focuses on the performance of existing, occupied buildings, assessing operational energy use, management practices, and adaptation. New build BREEAM assessments focus on the design and construction of buildings before they are occupied.

Can this calculator predict future energy savings?

This calculator estimates current performance based on input data. It doesn’t directly predict savings, but by comparing current EUI to benchmarks or simulating post-retrofit scenarios (by changing inputs), you can estimate potential savings.

What is considered a ‘good’ EUI?

A ‘good’ EUI varies significantly by building type, climate, and age. For instance, a modern office building might aim for under 30 kWh/m²/year, while a hospital could be over 150 kWh/m²/year due to intensive services. BREEAM provides specific benchmarks for various building types.

Does BREEAM In Use energy assessment include renewable energy generation?

Yes, BREEAM In Use considers on-site renewable energy generation. The assessment typically looks at both gross energy consumption and net energy consumption (after accounting for on-site renewables). Our simplified calculator focuses on gross consumption for clarity.

How often should I use a BREEAM In Use energy calculator?

It’s recommended to use the calculator annually, or whenever significant changes occur in building operations, systems, or occupancy. Regular assessment allows for tracking improvements and identifying new areas for optimization.

What if I don’t have precise energy data?

If precise data is unavailable, use the best available estimates from utility bills. For areas with no sub-metering, you might need to estimate based on equipment ratings and operating hours, or consult with a facilities manager or energy specialist. BREEAM provides guidance on estimation methods.

Related Tools and Internal Resources

• Sustainability Assessment Guide
  Learn more about comprehensive building sustainability evaluations beyond just energy.
• HVAC Efficiency Calculator
  Explore tools specifically designed to assess the performance of heating and cooling systems.
• Commercial Building Energy Benchmarking
  Understand how your building’s energy use compares to industry averages.
• Renewable Energy Integration Guide
  Discover options for implementing solar, wind, and other renewable energy sources in your building.
• Facility Management Best Practices
  Find tips and strategies for optimizing building operations and maintenance.
• Building Retrofit Planning
  Get insights into planning and executing energy efficiency upgrades for existing buildings.