3300 ACM Installation and Operation Manual Power Measurement Ltd.
Measured Parameters 4-5
Thermal Demand Measurements
The 3300 ACM provides a large number of optional thermal
demand measurements. Thermal demand values are calcu-
lated for real-time measurements using a method which is
equivalent to thermal averaging. For thermal averaging, the
traditional demand indicator responds to heating of a thermal
element in a Watt-Hour meter. The thermal demand period is
determined by the thermal time constant of the element,
typically 15 to 30 minutes. The demand period is the period
of time it would take the demand to ramp up to approxi-
mately 63% of the steady-state value (see Figure 4.3.1).
For thermal demand, the programmable demand period is
equal to the product of the following 2 parameters:
DEMAND PERIOD x # OF DMD PERIODS
This allows the user to match the power utility’s demand
calculation technique.
Each thermal demand measurement can optionally have
associated minima/maxima parameters available.
NOTE
On the front panel display, thermal de-
mand parameters are indicated using the
label DMD. For example:
kW DMD = kW thermal demand
TIME
63%
100%
DEMAND
0%
DEMAND PERIOD
LOAD
PARAMETER &
PARAMETER
DEMAND
Figure 4.3.1 Thermal Demand Calculation
4.3 MEASUREMENT MODES
Some optional measured parameters provide additional
measurement modes which are accessible from the front panel
using the FUNCTION button. The modes available to the
user are dependent on the parameter type, and the measure-
ment options with which the 3300 ACM has been equipped.
Figure 4.1.1 lists all modes applicable to each measured
parameter.
4.3.1 DEMAND
Introduction
Power utilities generally bill commercial customers based on
both their energy consumption (in kWH) and their peak usage
levels, called peak demand (in kW). Demand is a measure of
average power consumption over a fixed time period, typically
30 minutes. Peak (or maximum) demand is the highest
demand level recorded over the billing period.
Demand measurement methods and intervals vary between
power utilities. Some common methods include: thermal
averaging, sliding window, and fixed interval techniques. The
3300 ACM can perform demand calculations using both the
thermal averaging and sliding window demand techniques.
Courtesy of NationalSwitchgear.com
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