Understanding the Energy Performance Index
The Energy Performance Index (EPI) is an important metric used in building design and construction to measure the energy efficiency of a building. It is essentially a ratio that measures a building’s annual energy consumption in kilowatt-hours per square meter of the building. By calculating the EPI of a building, designers and builders can identify how energy-efficient a building is and take steps to improve its energy performance.
To calculate the EPI of a building, the annual energy consumption is divided by the total area of the building, excluding the area of unconditioned basements. The formula for calculating EPI is as follows:
EPI = Annual energy consumption in kilowatt-hours / Total building area (excluding unconditioned basements)
The EPI is typically used to comply with building codes and standards, such as the Energy Conservation Building Code (ECBC) in India. To comply with the ECBC, the EPI is calculated using either the prescriptive method or the whole building performance method.
The prescriptive method involves following specific design and construction requirements for the building envelope, lighting, heating, ventilation, and air conditioning (HVAC) systems. If the building complies with these requirements, it is deemed to have an EPI equal to that of a standard building with the same floor area, gross wall area, and gross roof area. The EPI ratio for the prescriptive method is always equal to 1.
The whole building performance method involves using computer simulations to model the energy consumption of the building and compare it to a standardized building with the same floor area, gross wall area, and gross roof area. If the building’s energy performance is equal to or better than the standardized building, it is deemed to comply with the ECBC. The EPI ratio for the whole building performance method should be less than or equal to the EPI ratio listed in §9.5 for the applicable building type and climate zone.
It is important to note that the EPI ratio is a relative measure of energy performance, comparing the energy consumption of the proposed building to that of a standardized building. Therefore, it is essential to use the same building type and climate zone when comparing the EPI ratio of different buildings.
In conclusion, the Energy Performance Index (EPI) is a crucial metric used to measure the energy efficiency of a building. It is calculated by dividing the annual energy consumption by the total building area, excluding the area of unconditioned basements. Compliance with building codes such as the Energy Conservation Building Code (ECBC) requires either the prescriptive method or the whole building performance method. By calculating the EPI of a building, designers and builders can identify opportunities to improve energy efficiency and reduce energy consumption, contributing to a more sustainable built environment.
Energy Performance Index (EPI) is a widely used metric for measuring the energy efficiency of a building. It is the ratio of the total energy consumed by a building to its total built-up area. A lower EPI indicates a more energy-efficient building. In this article, we will discuss step by step method for EPI calculation using the following example:
Residential Total Area = 60159 sq.m. ((50643+9516) sq.m) Retail Total Area = 9516 sq. m. Club Total Area = 3475 sq.m. GRIHA Benchmark EPI (For Air-Conditioned Residential Building) = 200 kWh/m2/yr GRIHA Benchmark EPI (@daytime used) (For 5 day/weeks occupied Air Conditioned Commercial) = 140 kWh/m2/yr
Step 1: Calculate the Benchmark EPI for the Project Benchmark EPI for the Project = (140*(9516+3475)) +(200*(50643+9516))/ (50643+9516+9516+3475) = 189.33 kWh/m2/yr
In this step, we are calculating the benchmark EPI for the project. We are using the GRIHA benchmark EPI values for air-conditioned residential and commercial buildings. The total built-up area of the project is 73150 sq.m. We are multiplying the total built-up area of the retail and club buildings with the commercial EPI and the total built-up area of the residential building with the residential EPI. We are then adding the two values and dividing it by the total built-up area of the project.
Step 2: Calculate the Designed EPI for the Project Total Energy Consumption (Excluding Miscellaneous) = 8272.4 MWh Total Area = (50643+ 9516 + 9516 + 3475) sq.m. = 73150 sq.m. Designed EPI for the Project = (Total Energy Consumption / Total Area)*1000 = (8272.4 / 73150)*1000 = 113.08 kWh/m2/yr
In this step, we are calculating the designed EPI for the project. We are using the total energy consumption of the project, which is excluding miscellaneous energy consumption. The total built-up area of the project is 73150 sq.m. We are dividing the total energy consumption by the total built-up area of the project and multiplying it by 1000 to convert it to kWh/m2/yr.
Step 3: Compare Designed EPI with Benchmark EPI Designed EPI for the Project = 113.08 kWh/m2/yr Benchmark EPI for the Project = 189.33 kWh/m2/yr
In this step, we are comparing the designed EPI with the benchmark EPI. The designed EPI for the project is 113.08 kWh/m2/yr, and the benchmark EPI for the project is 189.33 kWh/m2/yr. We can see that the designed EPI is significantly lower than the benchmark EPI, which indicates that the building is more energy-efficient than the benchmark.
Conclusion: EPI is an essential metric for measuring the energy efficiency of a building. In this article, we discussed the step by step method for EPI calculation using an example. We calculated the benchmark EPI and designed EPI for the project and compared the two values. The designed EPI was found to be significantly lower than the benchmark EPI, indicating that the building is more energy-efficient than the benchmark. EPI calculation can help architects, engineers, and building owners in designing and operating energy-efficient buildings.