Calculations Related to Energy Audits – Higher Engineering Science SQA Revision

Understanding Energy Audits

An energy audit is an assessment that shows where and how energy is being used in a facility, and identifies opportunities to improve energy efficiency.
This audit mainly consists of data collection, analysis and planning of energy saving measures.
Energy audits are done to reduce energy consumption which in turn reduces energy costs and decreases environmental damage.

The main unit of energy is the joule (J), but kilowatt-hours (kWh, a unit of energy used by electricity suppliers) are often used in practice.
Power is the rate of energy transfer, measured in watts (W). One watt is equivalent to one joule per second.
Efficiency is the ratio of useful output energy (or power) to input energy (or power), usually expressed as a percentage.
Energy transfer refers to the movement of energy from one place to another.

To find the energy usage: Energy (J) = Power (W) x Time (s).
To convert kWh to joules, multiply by 3.6 million (since 1kWh = 3.6 million joules).
To calculate power: Power (W) = Energy (J) / Time (s).
Efficiency can be calculated as: Efficiency (%) = (Useful energy output / Total energy input) x 100.

Specific energy consumption (SEC) is a key calculation in energy audits. It’s the energy consumption of a system, per unit of a relevant output factor (e.g., produced goods, heated/cooled space).
SEC can be used to compare energy efficiency across different systems or to track the energy performance of a system over time.
Estimated energy use can be calculated from known values or specifications for average power use and operating hours.

Potential energy savings can be calculated based on proposed energy efficiency measures.
The payback period for investment in energy saving measures can be calculated as the cost of the measure divided by the annual cost saving.