The bulk of buildings lack operational performance data, which means that proper management is almost impossible. Jim Sinopoli, managing principal of Smart Buildings, looks at various technologies to obtain data in order to manage the electrical load.
Electric meters
There are generally two types of power meters for buildings. One is for monitoring and measuring power to the entire building, while the other is a sub meter. The latter is to measure usage for specific spaces, tenants or electrical circuits, mainly to allocate or ‘back-bill’ the cost of electricity to consumers.
Sub meters include a current transformer (CT), a monitoring device resembling a doughnut that is locked onto individual electrical circuits at an electrical panel. The CT senses and gathers data on voltage, wattage and amperage on the circuit 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. Sub meters provide information on energy consumption based on kilowatt hours (kWh).
However, the monitoring of critical equipment such as switchboards and switchgear is much more sophisticated than sub meters, which gather data on a range of electrical characteristics to monitor power quality and provide diagnostics.
Metering and sub metering allow customers to effect operational changes so as to reduce energy consumption.
For example, if the data from a meter indicates a large electric load in an unoccupied building, there may be equipment running that needs to be shut down. The data may also reveal that shifting certain equipment schedules will reduce charges from utility companies by eliminating demand in peak periods.
Energy use indices (EUIs), such as kilowatt hours used per square foot (kWh/SF) can be compared between similar buildings to gauge if any particular building is using more energy than necessary. EUIs can also be compared to previous data to ascertain if a particular building’s energy usage has increased. Since equipment efficiency tends to decrease over time, observations of energy usage can indicate when equipment is in need of service or replacement.
Furthermore, a power management software application will transform the metering data into actionable information in order to supply trending data and allow for a ‘bill-back’ capability, as well as to identify sources of peak demand charges and power quality problems.
There are companies that can ‘read’ meters remotely and provide the owner or facility manager with Web-based access to energy-cost tracking tools and relevant data, thus obviating the need for procuring and maintaining costly software and hardware.
‘Smart’ power strips
Standby or ‘vampire’ power is electrical power consumed by electronic devices that have been turned off, or which are in ‘standby’ mode. International studies have revealed that the consumption of electrical power due to ‘standby’ mode is in the region of 7% to 13%. For example, the US Department of Energy estimates that about 75% of the electricity used to power home electronics in the average home is consumed while these products are turned off.
These devices are typically fed by a power strip with some surge protection. Such power strips have become incrementally ‘smarter’ by incorporating micro-processors, thus allowing the strips to ‘sense’ the electrical current, and to monitor and manage the plug load.
‘Smart’ power strips incorporate meters so as to provide information to users regarding energy consumption.
Some can even supply information on energy costs and power quality, including voltage, line frequency and power factor. ‘Smart’ power strips are finding increasing favour in data centres, where rack-mounted power strips feed servers, network switches and other equipment. These power strips have an IP Ethernet port allowing managers to monitor, manage and reboot equipment intelligently.
Power over Ethernet (PoE)
“PoE is probably the most under-valued technology is buildings,” argues Sinopoli. It not only moves devices from high to low voltage, and provides both power and communications through a single cable, but it can centrally monitor the devices. Several major IT manufacturers have developed software to manage the power to such devices, either turning them on or off, or even ‘dimming’ the power, much like the function of lighting control systems.
The management software essentially enables and disables PoE ports on a network switch. The result is a reduction in peak energy demand for IT networks, and the flexibility for network managers to set different power consumption for levels for various IT devices.
The management software typically comprises a module in a larger suite of network management tools, with capabilities to scale from one network to an entire enterprise. As the devices in question are already on an IT network, monitoring is done by means of SNMP tools to evaluate any device defined by a Management Information Base (MIB).
Some metering tips
• Plan and test: Target a couple of building spaces where consumption may be excessive. Use these as test beds before a full-scale deployment;
• Include three-phase HVAC load and in-building distribution transformers;
• Check the installation of CTs: The most common mistake is installing these backwards; and
• Obtain real-time data: This is a must in identifying potential problem areas and avoiding peak demand charges.