What We Measure And Why
The Watts Aware real-time power-use monitoring solution measures electrical current passing
through supply cables instrumented with the included current sensors. The actual electrical
power used is related to the current passing through the supply cables but also involves
other factors including the magnitude of the voltage "pushing" the current through these
supply cables and the power factor associated with your electrical load.
Watts Aware does not measure the voltage or the "power factor" but allows the user to
enter static values for the voltage and power factor for each sensor. Typically the voltage
is a fixed value such as 120 VAC, 220 VAC, 480 VAC or some other common value.
The "power factor" is more complex and depends on the details of the electrical load connected
to your instrumented supply cables. The electrical characteristics affecting the power factor
include whether the load is linear or non-linear and whether the load is capacitive or
inductive. An electrical load consisting entirely of incandescent light bulbs will be a linear load
and have a power factor of 1.0 while an electrical load consisting mostly of motors may also be a
linear load but have a power factor around 0.65, depending on the design of the motor
drive electronics. Although both of these examples are considered "linear" loads, in which relatively
little harmonic distortion is created, their power factors can be significantly different.
An example of a non-linear electrical load may consist of many "switching
power supplies", like those found in computers. These types of loads can significantly
increase the total harmonic distortion. This effectively reduces the power factor.
The cost of electricity at any instant for each kilowatt hour of consumption is dependent
on the details of the billing agreement between the user and the local electricity provider.
Many of these agreements include a variety of complex conditions: fixed monthly costs,
additional costs associated with the maximum power demand during the prior months,
different costs for using power during different times of the day, costs for presenting
different power factors to the utility's main electric service connection, and other special
cost factors. For many users, there is no single aggregate cost factor that can be applied
precisely to an increase or decrease in kilowatt hour usage.
It is difficult to include all cost factors in an "off-the-shelf" product since many of
these billing features require custom programming. The Watts Aware product uses general
rules to provide an approximation to the actual costs per kilowatt hour of delivered power.
Although these approximate costs may not be precise, the Watts Aware system correctly tracks
usage trends and is usually within a factor of 0.8 to 1.2 of the actual accounting costs
for the userís power. Sensor Synergy made these approximations to provide an easy to use,
easy to install, low cost, off-the-shelf product that can provide valuable information
to reduce power costs and identify the relative consumption of power using components.