energy usage in response to these price changes can save electricity customers a
great deal of money. Smart meters allow customers to monitor these price
changes and change their consumption if they choose.
Submetering is extremely helpful for understanding the way that energy is
used in a particular building or area. Utilities often install a single electricity
meter for an entire group of buildings which serves their purposes but does
not provide any information to the customer about load distribution among
different areas or buildings.
Without submetering a utility bill is often allocated according to the square
feet of occupied building space. With the use of submeters, payments for utili-
ties are based on measured usage, so there is an incentive for building occu-
pants to conserve utility resources.
A submetering system typically includes a “master meter” and a number of
submeters. The master meter is owned by the utility supplying the electricity
with overall usage billed directly to the property owner. Submeters are typi-
cally installed by the customer to provide data on energy usage by area, allow-
ing the customer to pinpoint buildings or spaces that use the most energy and
need attention. Submeters can be used for billing, an example being an apart-
ment building where tenants are billed individually for their electricity use.
Submeters typically have a couple of components to their deployment. One
is a current transformer or “CT.” The CTs are monitoring devices that look
like a donut and lock on to individual electrical circuits at an electrical panel.
The CT senses and gathers data on voltage, wattage and amperage on the cir-
cuit in real time or near real time. Multiple CTs will connect to a processor or
a server/controller with the processor having a connection to an IP or BAS
control network.
Typical communications protocols are Modbus TCP, SNMP MIB over an
Ethernet connection, Modbus RTU over an RS-232 connection, and BACnet
over an RS-485 network. Submeters are generally meant to provide informa-
tion on energy consumption based on kilowatt hours (kWh).
Metering and submetering allow customers to make changes in their opera-
tions that reduce energy consumption. For example, if the data provided by a
meter show that a large electric load exists when a building is unoccupied,
there may be equipment running that needs to be shut off. The data may also
show that shifting certain equipment schedules will reduce charges from utility
companies by eliminating demands during peak periods.
Energy use indices (EUIs), such as kilowatt-hours used per square foot
(kWh/SF), can be compared among similar buildings to determine if a building
is using more energy than it should. EUIs can also be compared to previous
data to see if the building’s energy usage has increased. Since equipment
efficiency tends to decrease over time, observations in energy usage can indi-
cate when equipment is in need of service or replacement.
66 Smart Building Systems for Architects, Owners, and Builders