ASHRAE Journal - April 2011 - 24

CritiCal Power CirCuits
Service Entrance Power Quality Enabled Circuit Monitor Circuit Monitor Circuit Monitor G Generation Point Circuit Monitor G Generation Point Circuit Monitor Circuit Monitor Circuit Monitor Power Quality Enabled Circuit Monitor

Circuit Monitor

Mains/Feeders

Circuit Monitor

Circuit Monitor Power Meter

seCondary Feeders

Power Meter UPS

Power Meter

Power Meter Power Distribution Unit

Power Meter

BranCh CirCuit/tenant Metering
Energy Meter

Energy Meter

Figure 1: Typical metering points in a power distribution system.

Metering vs. Submetering
No hard and fast definitions are known for these terms. Submetering is typically thought of as an element of branch circuitlevel monitoring through device monitoring—such as monitoring an individual piece of equipment or an end-user device. The size of power monitoring systems will vary from one installation to another. Small systems often include metering of the service entrance(s) only, whereas campus environments often include additional monitoring points in every building, as well as individually submetered branches or devices. Ultimately, the size and complexity of a metering system will depend on its purpose. For instance, submetering provides the ability to monitor individual tenants with regard to their energy consumption in order to bill them accordingly. Or, submetering may be used to determine how much energy individual chillers use, flagging unusual use that might be attributable to malfunctioning equipment. Submetering provides actionable information for decision-makers.

Manual correction involves addressing flagged data points and changing values through a data editing tool. Automatic data correction can take many forms, using data interpolation to correct for data jitter, duplicates, and nulls and voids. Whether imposed manually or automatically, all changes to the data in an energy monitoring system must have a complete audit trail to identify who made the changes-and when.

Weighing the Differences
More than one way exists to achieve the desired outcome: usable information for decision-makers. For example, a power utility metering system plays a vital role in a strategic energy action plan by ensuring that the initial energy and cost savings do not erode over time. Power meter installations, monitoring services, energy efficiency analysis and energy bill verification help achieve this goal. Another effective alternative is an enterprise energy management (EEM) system, which provides energy-related business intelligence for stakeholders and offers one of the most effective ways to maintain benefits from a strategic energy action plan. Essentially, an EEM system collects energy-relevant data pertaining to consumption of things such as water, compressed air, electricity and natural gas; it also considers other factors such as steam values, energy production information and outside air temperature. An EEM system collates all the information and then presents it to stakeholders in the form of actionable business intelligence in a customizable dashboard.
ashrae.org April 2011

Why Data Quality Matters
Enterprise-level systems often fail as a result of poor data quality. Problems with data quality can then lead to incorrect information or conclusions—or even to premature system abandonment. Data quality engines within a submetering system run data validation routines on a user-defined schedule. The system identifies potential data quality problems, as well as missing data, that can be corrected manually or automatically.
24 ASHRAE Journal

ASHRAE Journal - April 2011

Table of Contents for the Digital Edition of ASHRAE Journal - April 2011