Introduction

Monitoring and controlling the energy use of a building are two critical processes which should be incorporated in an energy management scheme.  These processes help to identify the overall efficiency and performance of a building.  Measuring the overall performance of a building, in terms of its energy consumption, is a highly necessary procedure.  Faulty equipment, inefficient operation or poor energy management behaviour can be identified and altered in aim of achieving a better energy flow in a building. 

It is important to find the source of the problems arising within an energy system in a building.  Any faults arising will add to the total energy bill being received by the company; and it is even more important to realise that an inefficient system will be increasing the severity of the impact on our natural environment.

A reduction in profitability is a considerable financial disadvantage for a commercial building such as a hotel; but aside from the financial losses that will be made, the inefficient use of energy and poor energy monitoring will have consequences far worse.  These consequences include a rise in greenhouse gas emissions in an ever-growing urban environment; further reduction of diminishing natural resources; and the potential benefits gained from sustainable urban development will be reduced.

Energy Management Strategies for Buildings

In order to maximise the benefits that can be gained from energy management, it is important to implement a set of strategies to help organise the management system.  These involve the following:

This involves reviewing the type of fuel that is being used and the associated tariffs.  In addition to this, developing and training a team of people to carry out and maintain a good practice scheme in the building environment;

By gaining control of the energy consumption in the building, a standard performance benchmark can be achieved.  Problems arising will be more recognisable by comparing costs, energy consumption levels and engineering systems within the building to the set standards.

Reviewing and maintaining high operating conditions for equipment being used; introduce new energy saving technologies into the building infrastructure to help reduce and/or increase efficiency of engineering systems. The impact of improvements introduced to the building infrastructure should only be based on the performance standards that are set after the initial energy survey carried out on the building.

Establishing energy monitoring teams within an organisation will increase the level of awareness and responsibility within a company; and therefore potential problems arising will be realised and resolved much sooner.

Part of the review process involves collecting reliable consumption data in order to carry out energy analysis studies.  There are several methods available to analyse the energy consumption data for the past and present; and in addition to this, future consumption predictions can be made.  The methods available include Regression Analysis; CUSUM (Cumulative Sum Deviation Method) Analysis; and Benchmarking standards based on Normalised Performance Indicators (NPI’s).  

All of these techniques will help to ensure that technical problems or poor building performance are identified.    

The review processes mentioned should be maintained and carried out on a regular basis throughout the lifetime of the building.

Analysis Techniques

Benchmarking

This performance indicator is based on expressing the buildings performance in terms of kWh/m2/year or m3/year.  The performance indicators calculated for gas and electricity consumption should be normalised according to climatic data and exposure coefficients; and other factors such as occupancy.

When these values are calculated they can be compared to published building performance standards to gauge the current level of energy efficiency; and what areas need to be investigated further in order to improve the performance.

The further analysis involves carrying out Regression and CUSUM Analysis, which are described below.

Regression Analysis

Regression Analysis is a statistical technique which can be used to determine the relationship between variables.  The time element of basic performance analysis is discarded in this method and instead the analysis is simply focussed on aspects of the buildings operation that affect the level of energy and resource consumption.  The most relevant building variables which are analysed are Electricity, Gas and Water.

These three variables are usually considered to be the ‘dependent variable’, and are used to investigate the level of influence between their consumption and other factors known as ‘independent variables’.  One of the independent variables used is Degree Day data (which provide a measure of the variation in outdoor temperatures in order to relate to the equivalent amount of energy being used).  The data can be plotted on a graph, producing a performance equation.

The regression analysis performed will show the level of significance between the energy or resource consumed and the independent variable used.  A number of reasons can account for a low correlation between the two variables.  The data being used must be accurate and reliable; a technical problem may exist within an engineering system e.g. heating system; and there may be other variables required for the regression.  The latter can be proved by carrying out multiple variable regression analysis.

Alternatively the regression can provide a good correlation between the variables analysed.  The performance equation produced can therefore be used to assess future consumption levels. 

CUSUM Analysis

The CUSUM Analysis method can be used to highlight the variation in a buildings performance over a specified period of time.  It involves a cumulative summation of the difference calculated between the actual consumption and the consumption calculated using the performance equation found from the regression analysis.

These points will then be plotted on a graph against the specified time period.  The slope of the graph generated indicates the level of efficiency in the building being investigated.  Slopes going up the way over time indicate poor performance; horizontal lines indicate that there is no change in the buildings performance; and slopes going down the way highlight good performance and increasing energy efficiency. 

By recording the dates of installed energy saving methods, the changes in the slope of the CUSUM graph could potentially be linked to that date; indicating that the change has had an impact on the buildings performance.