What a Building Energy Audit Is
A building energy audit is a systematic assessment of how a building uses energy, where waste occurs, and what cost-effective measures can reduce consumption. Energy audits range from basic walkthroughs that identify low-cost improvements to detailed engineering analyses that model complex system interactions and provide investment-grade recommendations. The audit establishes a baseline, identifies Energy Conservation Measures (ECMs), estimates savings and costs, and prioritises implementation based on return on investment.
Why It Matters
Energy typically represents 30-40% of a commercial building's operating cost. In Bangladesh, where electricity tariffs have increased significantly and power reliability remains a concern, energy management is both a cost and operational issue. A well-executed energy audit typically identifies 15-30% savings potential, with payback periods of 1-5 years for most measures. For organisations with ESG commitments, energy audits provide the baseline data needed for carbon reduction planning and reporting under frameworks like GHG Protocol, TCFD, and Science Based Targets initiative (SBTi).
ASHRAE Audit Levels
Level I — Walk-Through Analysis: A brief on-site survey of the building's major energy-using systems combined with utility bill analysis. Takes 1-2 days for a typical office building. Identifies no-cost and low-cost measures (scheduling adjustments, setpoint changes, lighting upgrades). Provides rough estimates of savings potential. Cost: typically USD 2,000-5,000 for a medium office building.
Level II — Energy Survey and Analysis: A more detailed evaluation including equipment inventory, operating schedules, building envelope assessment, and engineering calculations. Takes 1-2 weeks. Provides specific ECMs with detailed savings calculations, implementation costs, and simple payback periods. Includes utility rate analysis and load profiles. This is the most commonly requested audit level. Cost: typically USD 10,000-25,000.
Level III — Detailed Analysis of Capital-Intensive Modifications: Investment-grade analysis focusing on major capital projects. Includes hourly building energy simulation (using tools like EnergyPlus or eQUEST), detailed engineering design, accurate cost estimation, and financial analysis including life-cycle costing. Required when the building owner needs bankable savings projections for financing decisions. Cost: typically USD 25,000-75,000+.
Key Areas Assessed
HVAC Systems: Chiller efficiency (kW/ton), air handling unit performance, duct leakage, control strategies, economiser operation, variable speed drives, and part-load performance. HVAC typically accounts for 40-60% of total building energy in tropical climates like Bangladesh.
Lighting: Installed lighting power density (W/m2), lamp types and efficacy (lm/W), control strategies (occupancy sensors, daylight harvesting, scheduling), and task vs ambient lighting ratios. Lighting typically accounts for 15-25% of building energy. LED retrofits with smart controls often offer the fastest payback.
Building Envelope: Wall and roof insulation (R-values/U-values), glazing performance (SHGC, U-value), air infiltration, and shading effectiveness. In Dhaka's hot-humid climate, solar heat gain through glazing is a major cooling load driver.
Plug Loads and Equipment: IT equipment, kitchen appliances, process loads, and miscellaneous plug loads. Often the fastest-growing energy category, particularly in office buildings with high IT density.
Domestic Hot Water: System type, storage temperature, distribution losses, and usage patterns. Often a minor category in Dhaka but significant in hospitality and healthcare.
Power Quality and Distribution: Transformer losses, power factor, harmonics, and distribution efficiency. Poor power factor results in penalty charges from utilities and increased losses.
Energy Performance Metrics
Energy Use Intensity (EUI) is the primary benchmark: kWh per square metre per year. Good practice for offices in tropical climates is 150-200 kWh/m2/year; many Dhaka buildings operate at 250-400+ kWh/m2/year. Other key metrics include chiller system efficiency (0.6-0.8 kW/ton is good for centrifugal), lighting power density (target 8-10 W/m2 for offices), and cooling load intensity (200-300 W/m2 peak for offices in Dhaka).
Acting on Audit Findings
Prioritise ECMs by payback period: implement no-cost operational changes immediately (setpoint adjustments, schedule optimisation), then low-cost measures within 6 months (LED retrofits, VSD on pumps), and plan capital projects for the next budget cycle (chiller replacement, BMS upgrade, envelope improvements). Track implemented measures against predicted savings using Measurement and Verification (M&V) per IPMVP (International Performance Measurement and Verification Protocol).
Bangladesh Context
Energy audits in Bangladesh must account for generator fuel consumption alongside grid electricity, as most commercial buildings rely on backup generation for 2-8 hours daily. Utility bill analysis should separate grid and generator costs. The Bangladesh Energy Regulatory Commission (BERC) sets tariff structures that affect savings calculations. Available energy efficiency products and qualified contractors should be confirmed during the audit to ensure recommendations are implementable locally.
Standards and References
Key standards include ASHRAE Procedures for Commercial Building Energy Audits, ASHRAE Standard 90.1 (Energy Standard for Buildings), ISO 50002 (Energy Audits), ISO 50001 (Energy Management Systems), the International Performance Measurement and Verification Protocol (IPMVP), and LEED v4.1 Energy and Atmosphere credits. The Bureau of Energy Efficiency (BEE) India energy audit methodology is also relevant for the South Asian context.