A discussion topic during the Summer School was energy monitoring and targeting (M&T) and building energy management systems (BEMS). This blog provides an overview of energy monitoring and targeting 

1.0 Introduction

Energy monitoring and targeting is the collection, interpretation and reporting of energy use. Its role within energy management is to measure and maintain performance and to locate opportunities for reducing energy consumption and cost [1].

Traditionally energy monitoring and targeting has two principal functions :

(i) The on-going control of energy usage

(ii) Improvements in the efficiency of energy usage by setting targets

The benefits of energy monitoring and targeting include: 

• Energy consumption and cost savings, typically 7-12%.
• Reduction of the environmental impact of energy usage.
• Providing energy information for assessing energy projects and new plant acquisitions.
• Improving preventative maintenance.
• Waste avoidance and improved product quality by increased level of control.

Figure 1 outlines the main components of an automatic energy monitoring and targeting (M&T) system.

Fuel Meters and Sensors: These collect data on energy/fuel loading and consumption.

Data acquisition unit: The data acquisition unit (which may be a BEMS) is used for receiving and archiving energy data from energy meters and sensors such as temperature and pressure. 

Communication Network: The network provides communication between the data acquisition unit and the central computer.

Central Computer: The central computer has software to upload data from the data logger and provide energy analysis.

2.0 Data Collection

Data may be automatically captured and key inputted into the energy information software system. The types of data collected may be categorised as energy data and energy drivers.

2.1 Energy Data:

Energy consumption data is automatically captured from energy meters. Energy consumption data, energy load data, and deduced costs are archived by the energy information software.

Energy data is monitored and collected for meters and for areas of accountability, generally termed an Energy Account Centre (EAC) within an energy site. The energy of an EAC should be measurable and manageable. An EAC, for example, could be a specific technology (e.g. lighting, compressed air), a department, a building, or an industrial production process.

Energy meters are usually categorised as follows:

Main Meter: A main meter is a supply meter for fuel supply (including electricity) to site.

Sub-Meter: A sub-meter is a meter installed after or down line from the main meter. Sub-meters are installed to measure energy with an EAC.

Virtual Meter: A virtual meter is a function of the measured energy from a number of other meters.

2.2 Energy Drivers:

An energy driver is a factor that influences the energy consumption and energy load levels overall and or for an EAC. Weather and occupancy are drivers that influence a standard office block. Production throughput, weather, and occupancy are drivers that may influence an industrial site. A common driver used in energy analysis is degree-days. Degree-days are used to compare building energy usage with the outside air temperature. Heating degree-days are the number of degrees by which the mean outside air temperature (over 24 hours) on each day was less than a given base temperature of 15.5°C.

3.0 Data Analysis

The data analysis undertaken may be divided into two categories, routine and investigative.

3.1 Routine Analysis

This type of analysis is provided on a periodic basis. The type of analysis provided includes: energy consumption, energy costs, energy performance and specific energy requirements for defined time periods e.g. daily, weekly, year to date. Performance analysis techniques commonly used in routine analysis are outlined in Table 1 below.

Table 1 Routine Energy Analysis

Benchmarks are widely used in industrial practice to improve performances through competition and comparison with others. Establishing Specific Energy Ratios and Normalised Performance Indicators (NPI) will allow the comparison of energy performance against good practice benchmarks and provide a guide as to how an organisation is performing.

3.2 Investigative Analysis

A list of common investigative techniques is provided in Table 2.2. The investigative techniques used are similar to those used in quality control statistics. Techniques employed utilise and combine linear regression, cumulative sum (cusum) charts, and control charts.

References

CIBSE, Building Control Systems CIBSE Guide H, Butterworth Heinemann, Oxford, 2006.

ETSU, GPG 31: Computer Aided Monitoring and Targeting for Industry, Energy Efficiency Office, Harwell, 1991.

ETSU, GPG 125: Monitoring and Targeting in Small and Medium Sized Companies, Energy Efficiency Office, Harwell, 1998.