## 1 Introduction
Wireless sensor networks generally contain thousands of sensor nodes, randomly deployed in a field. The sensor nodes are powered by batteries and controlled remotely. For many applications, the recharging or replacement of these batteries in the sensor nodes after deployment is impossible [9]. Depending on the use of sensor networks, certain routing protocols are required, in order to allow communication between sensor nodes and the sink nodes [10]. Wireless sensor networks consume a limited amount of energy in collecting data, performing calculations and routing the received data, so in most applications, each sensor node is expected to last for a long time [11]. For this reason, both the efficient use of energy and efficient routing schemes are highly important in sensor networks [9]. Published research has demonstrated effective ways of cutting energy use, through the development of new technology. If this strategy is successful, a reduction in the growth in energy consumption, as discussed in previously, can be achieved. However, before these new techniques can be practically applied, one technical issue must first be addressed, in that there must exist a means to quantitatively measure energy savings. Although power consumption before and after energy saving improvements are implemented can be tracked, the actual amount of energy saved is hard to determine. Figure 1 illustrates the problem. Figure 1: Before and after energy saving improvements, energy use is easy to measure and track, but energy savings cannot be measured, because the power consumption without those improvements cannot be determined. As illustrated in Figure 1, energy savings are difficult to measure, because the power consumption without the energy saving improvement is impossible to measure. Thus, most research related to the development of energy saving technology uses a comparison method. Energy use before and after applying the energy saving techniques is measured and compared, to determine the energy saved. The assumption is that the energy use before and after the improvements is the same. In the laboratory, conditions can be adjusted to concur with this assumption and accurate energy savings can be calculated. The comparison method works experimentally, but in real applications, where such adjustments are not possible, the energy savings reported by assuming unchanged energy use are not correct. A tool for measuring energy savings must report those savings by measurement. This is a key requirement for research related to energy saving technologies. Only if the energy saving effects can be verified accurately, can energy saving research provide real commercial products that ensure a low carbon future. In order to accurately estimate these energy savings, the internationally recommended International Performance Measurement and Verification Protocol (IPMVP) defines standard terms and suggests best practices for quantifying the results of energy efficiency investments and for increasing investment in energy and water efficiency, demand management and renewable energy projects [12]. The IPMVP was developed in 1994-1995 by a coalition of international organizations, led by the United States Department of Energy [13]. The Protocol has become the national measurement and verification standard in the United States and many other countries [13]. A major driving force for the standard was the need for a common protocol to verify savings claimed by Energy Service Companies (ESCs), when implementing Energy Conservation Measures (ECMs). The protocol is a framework to determine the water and energy savings associated with ECMs. IPMVP provides four options for the determination of savings (identified as A, B, C and D) [14]. Options A and B focus on the performance of specific ECMs and involve measuring the energy use of systems affected by each ECM, separately from that of the rest of the facility. Before and after measurements are compared, to determine savings. A lighting retrofit and installation of variable speed drives are examples of options A and B.