Book - School of Science and Technology

678 Running costsEnergy auditsAn energy audit is fundamentally a management tool to control energy use and costs. It isessential, in the first place, to analyse energy use; where, how much and in what form it isbeing expended. Then, consumption must be monitored at regular intervals, monthlybeing often the most convenient period, through the heating season and, where appropriate,through the cooling season. The results should then be compared with a suitableindicator for the same periods, such as degree days. Once the operator has a full understandingof how energy is being used, targets may be set with the aim of reducing usageand followed by detailed studies with intent to identify further savings. At this point itmay be beneficial to consult an expert in the field.The DETR (DEFRA since 2001) through their Energy Efficiency Best Practice programmeand CIBSE have both published guidance on the subject, and the DHSS Encode.Volumes 1 and 2, 1994 are useful references. For general information upon the efficientuse of energy in buildings, the reader is referred to the excellent publications produced bythe Building Research Energy Conservation Support Unit at the BRE.In carrying out such an audit, it is necessary to establish that, commensurate with the costof meeting the objective, the following criteria are met in the most energy efficient manner:. That the most economical source of energy is used and at the best commercial tariff.. That all energy is converted efficiently.. That distribution losses are minimised.. That patterns of demand are optimised and plant controls are compatible.. That energy recovery equipment is provided.A graphical representation of readings taken will identify significant variations from anestablished trend. Figure 23.5 (p. 684) shows a typical example of fuel oil usage againstdegree-days for two heating seasons, and as can be seen a straight line graph should beobtained. An alternative approach is to calculate for each month a litre/degree-day whichshould give a constant figure, subject to allowable practical tolerances. An annual litre/degree-day ratio, or an equivalent for different fuels, will provide also a means to compare theperformance of one building with another. This will quickly identify poor performance, forwhatever reason, and establish where improvements should be investigated as a first priority.Energy content of fuelsIt is useful to bring together a summary of energy availability from the various sourcesand Table 23.12 lists gross heat quantities provided by various fuels.Fuel prices are not given here because these will vary with the area of the country andwith market forces of the day. Prices can be readily obtained from the appropriate supplyauthorities.Environmental auditsEnvironmental issues are of ever growing public concern. The construction, use and demolitionof buildings have a major impact upon both the local and global environments, not theleast of which is concerned with the energy consumed by engineering services. The burningof fossil fuels not only depletes a finite resource but also produces carbon dioxide, the maincontributor to global warming, sometimes referred to as the greenhouse effect. Table 23.13lists information on the rate of carbon dioxide emission by combustion of various common