The granularity of energy data provided by submetering technology is becoming more and more appreciated by building managers and owners. However, it is important to note that the implementation of submetering is quite different from building level metering, and it is critical to identify the right technology to get you the most relevant and cost efficient data.
Implementing Real-Time Metering: Submetering vs. Building Level Metering
Building level metering is easily installed by utilizing preexisting utility company meters. The utility company will typically provide a KYZ interface for each utility meter, and an external gateway will “count” the pulses, and convert them to energy usage in KWh, by applying a multiplier.
In contrast, submetering usually requires more hardware and labor because the current and the voltage feeding the equipment both need to be measured. While current can be measured with clamps and doesn’t require power interruption, voltage measurement typically requires wire installation, which requires a temporary power outage. This method is more cumbersome and more expensive, so it is necessary to ensure that this technology is the right choice for your building before using it.
Submeter Installation Challenges
There are two main ways to measure voltage for real-time submetering, and they both have constraints. The first option requires a power outage before placing the voltage wires onto the source. This poses a challenge when trying to measure the power consumption of a large load feeding essential equipment that cannot be turned off easily without interrupting operation.
To avoid a major power outage, the second option can be used. The voltage can be read through a subpanel being fed by the main source where we want to measure power, since voltage measurement is the same at any point of the circuit as long there is not a transformer separating the source from the subpanel. Inside of the subpanel, a small breaker can be turned off to connect the wires from the voltage meter without causing any disturbance in building operations. Although this tends to be much better than the first option, there are still challenges. The downside of this solution is that a subpanel might be located far from the original source of power where the current transformer clamps are located. Consequently, wires and conduits will have to be run over long distances, which may increase the cost and complexity of the installation.
There is a rather large number of commercial grade meters available in the market. Nowadays, most of them offer some kind of networking capability. At the very least, they offer Modbus instead of a basic LCD screen. Some meters even have wireless capability, which reduces the cost of running Ethernet Cat-5 cable to the electrical room, and is generally the best option. In the era of the Internet of Things, it is highly recommended to choose building meters that are Internet-ready and are able to send data directly to the Cloud. This will reduce the hardware cost since no other gateway or server will be needed on site.
Submetering is an essential component in providing real-time energy monitoring for commercial buildings. However, since it is more complex than building level metering, it is important to target the right equipment, and to choose the proper hardware and installation configuration to minimize the setup cost.