By CUNY BPL on March 7, 2018
City University of New York
Systems of Interest
The gymnasium had 60 metal halide fixtures that consumed up to 1000W each. The retrofit was to replace the metal halide fixtures with 380W LED fixtures.
The lighting fixtures for the gymnasium were serviced by two lighting panelboards without automatic controls (dedicated panelboard without automatic controls). CUNY BPL decided to take direct measurements of AC current for both panelboards for several weeks.
This measurement strategy was chosen for two reasons:
- Because there were two panelboards it was easier to install the 4 channel analog loggers with Current Transducers since they took up less space inside the panelboard.
- We wanted to verify the hours of operation of the fixtures. By using the 4 channel analog logger we collected both the operating schedule of the fixtures and AC current of the panelboards.
When using the 4 channel logger to measure AC current we also needed to measure the Voltage and power factor to calculate power. We did this by using the Fluke 345 clamp meter to take spot measurements.
A onetime measurement of each incoming feed line was enough to give us the voltage (which should be the same for all three lines if the panelboard only serves lighting) and power factor.
“What’s the purpose of using a power clamp meter?”
The 4 channel analog logger with CT sensors only measures AC current and nothing else. To determine the energy consumption of the panelboard(s) you need to know the voltage for each line (assumed to be the same for a lighting panelboards) and the power factor. The clamp meter allows you to measure these parameters.
“What’s the purpose of the three phase power measurement?”
This setting measures power factor and Voltage for the entire panelboard. You can only use this setting if the panelboard is a balanced load (almost always for lighting systems).
“If all fixtures in the space have the same power draw why didn’t you use a Light on/off data logger?”
The light on/off data logger, used to determine the hours of operation of lighting fixtures, is the least accurate method to determine the energy consumption of a space or facility. The reason is that the light on/off data logger is used for proxy measurements instead of direct measurements which are more accurate. Yes we could have used the light on/off data logger but since the panelboards were dedicated to lighting, easily accessible and we had plenty of 4channel analog loggers and CT sensors, the better option was to take direct measurements ,specifically AC current. You should only resort to using the light on/off data logger if you have facility constraints such as, inability to access panelboard or panelboard is mixed with other loads and you are unsure of what circuit breakers serve the light fixtures.
What We Used
The 4 channel analog logger supports up to four external sensors allowing you to measure temperature, current, voltage, air flow, pressure and more in one single logger.
The clamp meter measures Power factor (PF), Reactive Power (VAR), Watt Hours (Wh), Kilowatt hours (kWh), AC Current, AC Voltage and more.