Apparent power is the total electrical power supplied to an AC circuit, measured in volt-amperes (VA). It combines both the real power (watts) that performs useful work and the reactive power (vars) that oscillates between the source and load. Apparent power is calculated by multiplying voltage and current: S = V × I.
Technical Details
Apparent power differs from real power by the power factor, which ranges from 0 to 1. The relationship is expressed as S = P / PF, where S is apparent power in VA, P is real power in watts, and PF is the power factor. This distinction becomes critical in HVAC systems operating at high reactive loads, such as motors and compressors that use 10 to 30 kVA of apparent power.
Practical Significance
Understanding apparent power is essential for proper electrical system design. Undersizing equipment based on real power alone can result in inadequate power delivery and system failures. Electrical utilities charge commercial HVAC customers based on both demand (in kW) and reactive power (in kVAR), making power factor correction economically important. Many HVAC contractors must account for 20 to 40 percent reactive power in compressor loads.