This paper presents the details of a recent study conducted to determine the relative cost-effectiveness of portable energy meters used to sub-meter Heating, Ventilating and Air Conditioning (HVAC) equipment for energy audits and/or for measurement and verification of retrofit projects. The results provide an insight as to how fluctuations in voltage and harmonic distortion (caused by variable speed drives) affect the accuracy of power measurements taken by current meters and relatively inexpensive (<$1,000) watt meters. The evaluation criteria for this study include data logger and sensor cost, power measurement accuracy, ease of installation within an electrical breaker panel, and ease of use of the software. The accuracy of the portable meters was tested for a motor controlled by a variable frequency drive (VFD). The operating range for each test included loads of 25 percent, 50 percent, 75 percent, and 100 percent of full load at 60 Hz and then at 50 Hz and 40 Hz with the corresponding load. Once the motor reached thermal stability at its rated output, power measurements were taken at the electrical panel with a laboratory-grade power analyzer and with each of the portable test meters.